The following symbols are used in this Product Information to improve
understanding and to highlight important information:
3 contains important safety information as well as information that is
necessary to ensure smooth system operation and must be adhered to.
1 identifies the end of a note.
Information status and national variants
BMW vehicles conform to the highest safety and quality standards.
Changes in terms of environmental protection, customer benefits and
design render necessary continuous development of systems and
components. Consequently, there may be discrepancies between this
Product Information and the vehicles available in the training course.
This documentation describes left-hand drive vehicles.
In right-hand drive vehicles, the arrangement of some controls or
components may differ from the illustrations in this Product Information.
Further differences may arise as the result of the equipment variants used
in specific markets or countries.
Additional sources of information
Further information on the individual topics can be found in the following:
- Owner's Handbook
- Integrated Service Technical Application.
Page 5
Contents.
Advanced Diesel.
Objectives
Product information and working reference for
practical applications.
Models3
Engine variants3
Introduction7
System components23
Engine mechanical system23
Air intake and exhaust system25
Cooling system38
Fuel preparation system41
Overview of fuel supply system43
Functions of the fuel supply system47
Components of the fuel supply system51
Overview of selective catalytic reduction60
Functions of selective catalytic reduction
system
Components of the selective catalytic
reduction system
Engine electrical system110
Automatic transmission119
72
95
1
1
Page 6
Page 7
6
Objectives.
Advanced Diesel.
Product information and working reference for practical
applications.
This Product Information provides information
on the design and function of the M57D30T2
US engine.
This Product Information is structured as a
working reference and complements the
subject material of the BMW Aftersales
Training seminar. The Product Information is
also suitable for self-study.
As a preparation for the technical training
program, this Product Information provides an
insight into the diesel engine for the US
market. In conjunction with practical exercises
carried out in the training course, its aim is to
enable course participants to carry out
servicing work on the M57D30T2 US engine.
Technical and practical background
knowledge of the current BMW diesel engines
will simplify your understanding ofthesystems
described here and their functions.
1
Page 8
6
2
Page 9
7
Models.
Advanced Diesel.
Engine variants
Models with the M57D30T2 US engine at the
time of market launch in Autumn 2008.
1 - BMW 335d2 - BMW X5 xDrive35d
3
Model
335dE90M57D30T2299390/84
X5 xDrive35dE70M57D30T2299390/84
Model series
Engine
Cylinder capacity in cm
Bore/stroke
in mm
Power in
kW/bhp at rpm
200/265
4200
200/265
4200
Torque in
Nm at rpm
580
1750
580
1750
Market launch
11/08
11/08
3
Page 10
7
History of the M57 engine
The M57 engine is by far one of the most
successful engines at BMW. It is fitted in
numerous models right across the vehicle
range. It plays the part of the extremely
powerful top-of-the-range engine, for example
in the 3 Series just as effectively as the wellbalanced entry class engine in the 7 Series.
10 years have already passed since its
introduction and many improvements have
been made during this period. In particular the
re-engineering that took place in 2002 and
again in 2005 ensure that the M57 engine is
still state-of-the-art.
The following table shows an overview of the
individual models equipped with the M57
engine.
M57D30O2730dE652993170/231520DDE6263/059/08
M57D30O2330dE902993170/231500DDE6269/059/08
M57D30O2330dE912993170/231500DDE6269/059/08
M57D30O2530dE612993170/231500DDE6269/05in production
M57D30O2530dE612993170/231500DDE6269/05in production
M57D30O2730LdE662993170/231520DDE6269/059/08
M57D30O2X3 3.0dE532993160/218500DDE6269/05in production
M57D30U2325dE902497145/197400DDE6069/06in production
M57D30U2325dE912497145/197400DDE6069/06in production
M57D30O2330dE922993170/231500DDE6269/06in production
M57D30T2335dE902993210/286580DDE6269/06in production
M57D30T2335dE912993210/286580DDE6269/06in production
M57D30T2335dE922993210/286580DDE6269/06in production
M57D30T2X3 3.0sdE832993210/286580DDE6269/06in production
M57D30U2325dE922497145/197400DDE6063/07in production
M57D30U2525dE602497145/197400DDE6063/07in production
M57D30U2525dE612497145/197400DDE6063/07in production
M57D30O2330dE932993170/231500DDE6263/07in production
M57D30O2X5 3.0dE702993173/235520DDE6263/07in production
M57D30T2535dE602993210/286580DDE6263/07in production
M57D30T2535dE612993210/286580DDE6263/07in production
M57D30U2325dE932497145/197400DDE6069/07in production
M57D30T2635dE632993210/286580DDE6269/07in production
M57D30T2635dE642993210/286580DDE6269/07in production
M57D30T2X5 3.0sdE702993210/286580DDE6269/07in production
M57D30O2X6
M57D30T2X6
Model
xDrive30d
xDrive35d
Model series
Cylinder capacity
in cm3Power output
E712993173/235520DDE6265/08in production
E712993210/286580DDE6265/08in production
in (kW/bhp)
Torque
in Nm
Engine
management
First used
Last used
5
Page 12
7
6
Page 13
8
Introduction.
Advanced Diesel.
A diesel engine for North America
Impressive power and performance as well as
exemplary efficiency have contributed to
making BMW diesel engines an attractive as
well as future-oriented drive technology. This
technology is now being made available to
drivers in North America.
BMW is introducing this diesel technology to
the USA and Canada under the name "BMW
Advanced Diesel". The introduction is an
integral part of the EfficientDynamics
History
In 1892, Rudolf Diesel applied for a patent for
his first self-igniting combustion engine.
Initially, this large, slow-running engine was
intended for stationary operation only. The
intricate engine structure and complicated
injection system meant production costs were
high. The first simple diesel engines were not
particularly comfortable and powerful-revving
machines. It was not possible to mistake the
distinctive sound of the harsh combustion
process in the diesel engine when cold (diesel
knock). Compared to thesparkignition engine,
it offered a poorer power/weight ratio,
acceleration characteristics and lower specific
output.
"Miniaturization" could be realized only by
improving materials and the manufacturing
process during the course of commercial
vehicle production. Although the first diesel
vehicle was presented as early as 1936, it was
not before the 1970s that the diesel engine
became accepted as a viable drive source.
The breakthrough came in the 1980s when
the diesel engine was finally refined enough to
be a real alternative to the spark ignition
engine. At this time, in view of the improved
dynamics and acoustics the decision was
development strategy, which has become a
synonym for extremely low CO2 emissions not surprising when considering its extremely
low fuel consumption. EfficientDynamics is
not solely an instrument for reducing fuel
consumption but rather it is designed as an
intelligent entity with increased dynamics. Not
without good reason theM57D30T2 engine is
referred to as the world's most agile diesel
engine.
made to introduce the diesel engine in series
production vehicles at BMW.
1 - Rudolf Diesel and his engine
7
Page 14
8
1983
The M21D24 engine introduced for the first
time in the E28 as the 524td featured an
exhaust turbocharger and had a displacement
of 2.4 litres. It was derived from the M20 6cylinder petrol engine and developed 85 kW/
115 bhp. Both engines could therefore be
built on the same production facilities.
At that time, the performance with a top speed
of 180 km/h and acceleration from 0 to 100
km/h in 13.5 seconds set new standards in the
dynamics of diesel motor vehicles. The 524td
was therefore given the nickname "Sport
diesel".
This was thefirst diesel engine at BMWand, at
the same time, the last for a long time in the
US market.
2 - BMW 524td with M21 engine
1985
The M21 was also built as a naturallyaspirated diesel engine as from September
1985, making it possible to offer a costeffective "entry-level engine". This engine
made a name for itself in the 324d (E30) as the
smoothest running auto-ignition engine on the
market.
1987
As the world's first carmaker to do so, BMW
introduced the electronic engine
management system, the so-called Digital
Diesel Electronics (DDE). Faster and more
exact than a mechanical control system, the
electronics effectively controls:
• Exhaust emission characteristics
• Fuel consumption characteristics
• Noise emission
• Engine running refinement.
8
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8
1991
1991 saw the debut of the newly developed
M51D25 engine which, with intercooling and
an output of 105 kW/143 bhp was the most
powerful diesel engine in its class throughout
the world. It replaced the M21 engine and was
3 - BMW 525tds with M51 engine
fitted with a crankcase based on a completely
new design.
The engine was offered in the output variants
115 bhp and 143 bhp. Exhaust emission and
full load smoke were reduced by a V-shaped
main combustion chamber in the piston.
1994
The M41 engine was the first4-cylinder diesel
engine to beused at BMW. It was derived from
the M51D25 engine and shared 56 % of its
components. New features included the
hollow-cast camshaft mounted in 5 bearings
as well as a cylinder head cover the isolated
structure-borne noise.
This engine was fitted in various models of the
E36 series.
9
Page 16
8
1998
In 1998 BMW built the most powerful 4cylinder diesel engine - the M47 with direct
fuel injection.
4 - BMW 320d with M47 engine
Motor sport provided the best proof of the
efficiency and reliability of the new diesel
technology. BMW celebrated a historic
success on the Nürburg Ring.
With 100 kW developed from 2 litre
displacement, a performance level was
achieved which up until then was the reserve
only of petrol engines. This corresponds to a
specific output of 50 kW or 68 bhp.
With the 320d, a diesel engine won a 24 hour
race for the first time in motor sports history in
1998. This victory came not only due to the
fact that it needed fewer pit stops for refuelling
but also because the BMW drove the fastest
lap times.
10
5 - BMW 320d touring car with M47 engine
Page 17
8
1999
The first V8 diesel engine, the M67D40
engine, with 4 litre displacement was
presented in the E38 which developed an
output of 175 kW. BMW proved its technical
authority with the, at that time, world's most
powerful passenger vehicle diesel engine with
6 - BMW 740d with M67 engine
common rail fuel injection and 2 exhaust
turbochargers.
The engine is fitted with a crankcase made
from high-strength cast iron with vermicular
graphite (GGV), an aluminium cylinder head
and a two-piece oil sump.
2001
The M47TU with the second generation
common rail injection system and DDE5
boosted the power output to 110 kW/150 bhp.
The M57D30 engine is a further development
of the M51D25 engine. It has a cast iron
casing fitted with a light alloy cylinder head
with 4-valve technology. The M57 engine is
the world's first 6-cylinder in-line diesel engine
in a passenger vehicle that is equipped with
future-oriented common rail injection
technology.
This new, highly complex electronically
controlled fuel injection system perfectly
satisfies the demands for high and constant
injection pressure over the entire injection
period. The engine offers substantially lower
fuel consumption compared to swirl-chamber
engines, superior performance and smooth
engine operation under extreme conditions.
11
Page 18
8
7 - BMW 530d with M57 engine
2004
The M57TU TOP engine with 2-stage
turbocharging is introduced as the most
powerful diesel engine (E60 and E61). One
small and one large turbocharger is usedin the
2-stage turbocharging system. The diesel
engine in the 535d develops 40 kW/54 bhp
more than at the same displacement (3.0
litres) in the 530d.
The power output is 200 kW/272 bhp. The
maximum torque of 560 Nm is reached at
2000 rpm. With this extraordinary engine, Luc
Alphand won not only the diesel classification
of the Paris-Dakar Rally, but also came fourth
in the overall rankings.
12
8 - BMW X5 3.0d with M57TU TOP engine
Page 19
8
2005
The M57TU2 engine is fitted in the E65. In
addition to the increase in output and torque,
it boasts the following technical features:
• Reduced weight through aluminium
crankcase
• 3rd generation common rail system with
piezo-injector and a fuel rail pressure of
1600 bar
• Compliance with the exhaust emission
regulation EURO 4 and diesel particulate
filter as standard
• Optimized electric boost pressure actuator
for the turbocharger with variable turbine
geometry.
9 - BMW 730d with M57TU2 engine
2005
The M67 engine in the E65 was
comprehensively reengineered in the same
year. The aim was to achieve a distinct boost
in dynamics by increasing power output and
reducing weight. In the case of the M67
specifically this aim is reflected in an increase
in power output of 16 % while simultaneously
reducing the engine weight by 14 % - and
achieved without increasing fuel consumption.
This was mainly achieved through a new,
lightweight aluminium crankcase and by
increasing the displacement to 4.4 litres.
13
Page 20
8
10 - BMW 745d with M67TU engine
2006
In 2006, the M57TU TOP engine was reengineered and equipped with the same
technical details as the M57TU2, such as an
aluminium crankcase and piezo-fuel injectors.
This engine was given the designation
M57D30T2. It was introduced simultaneously
into the 3 Series as the 335d and in the X3 as
the 3.0sd. This re-engineering resulted in
further-improved power characteristics,
enhanced smooth operation and a significant
reduction in fuel consumption. This engine
forms the basis for re-introducing diesel
technology into the USA after more than 20
years.
14
11 - X3 3.0sd with M57TU2 TOP engine
Page 21
8
Legislation
Since the first exhaust emission legislation for
petrol engines came into force in the mid1960s in California, the permissible limits for a
range of pollutants have been further and
further reduced. In the meantime, all industrial
nations have introduced exhaust emission
legislation that defines the emission limits for
petrol and diesel engines as well as the test
methods.
Essentially, the following exhaust emission
legislation applies:
• CARB legislation (California Air Resources
Board), California
• EPA legislation (Environmental Protection
Agency), USA
• EU legislation (European Union) and
corresponding ECE regulations (UN
Economic Commission for Europe), Europe
• Japan legislation.
This legislation has lead to the development of
different requirements with regard to the
limitation of various components in the
exhaust gas. Essentially, the following exhaust
gas constituents are evaluated:
• Carbon monoxide (CO)
• Nitrogen oxides (NOx)
• Hydrocarbons (HC)
• Particulates (PM)
It can generally be said that traditionally more
emphasis is placed on low nitrogen oxide
emissions in US legislation while in Europe the
focus tends to be more on carbon monoxide.
The following graphic compares the standard
applicable to BMW diesel vehicles with the
current standards in Europe. A directcomparison, however, is not possible as
• different measuring cycles are used and
• different values are measured for
hydrocarbons.
15
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8
12 - Comparison of exhaust
emission legislation
StandardValid fromCO
[mg/km]
EURO 401.01.2005500250300-25
EURO 501.09.2009500180230-5
EURO 601.09.201450080170-5
LEV IIMY 2005211031-476
* In Europe, the sum of nitrogen oxide and hydrocarbons is evaluated, i.e. the higher the HC
emissions, the lower the NOx must be and vice versa.
** In the USA, only the methane-free hydrocarbons are evaluated, i.e. all hydrocarbons with
no methane
Although the European and US standards
cannot be compared 1:1 it is clear that
requirements relating to nitrogen oxide
emissions are considerably more demanding.
Diesel engines generally have higher nitrogen
oxide emission levels than petrol engines as
NO
[mg/km]
HC + NOx*
x
diesel engines are normally operated with an
air surplus.
For this reason, the challenge of achieving
approval in all 50 states of the USA had to be
met with a series of new technological
developments.
[mg/km]
NMHC**
[mg/km]PM[mg/km]
16
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8
Overview of innovations, modifications and special features
The following table provides an overview of
the special features of the M57D30T2 US
engine. They are divided into various
categories.
• New development signifies a technology
that has not previously been used on BMW
engines.
• Modification signifies a component that was
specifically designed for the
M57D30T2 US engine but does not
represent a technical innovation.
• Adopted describes a component that has
already been used in other BMW engines.
This Product Information describes only the
main modifications to the M57D30T2 engine
compared to the Europe version as well as
fundamental vehicle systemsspecificto diesel
engines.
Component
Engine mechanical system7Very few modifications have been made to
Air intake and exhaust
system
Cooling system7In principle, the cooling system corresponds
Fuel preparation system7The functional principle of the fuel
New development
Modification
7The most extensive changes were made to
Remarks
Adopted
the basic engine. The modifications that
have been made focus mainly on ensuring
smooth engine operation.
A significant feature, however, is the OBD
monitoring of the crankcase breather.
the air intake and exhaust system. For
instance, low pressure exhaust gas
recirculation (low pressure EGR) is used for
the first time at BMW on the E70.
In addition to other minor adaptations, there
are substantial differences in the sensor and
actuator systems.
to that of the Europe versions, however, it
has been adapted to hot climate
requirements.
preparation system does not differ from that
of the Europe version, however, individual
components have been adapted to the
different fuel specification.
17
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8
Component
Fuel supply system7The fuel supply system is vehicle-specific
SCR system
(Selective Catalytic
Reduction)
Engine electrical system7The engine is equipped with the new DDE7
Automatic transmission7The automatic transmission corresponds to
New development
Modification
7The SCR system is used for the first time at
Remarks
Adopted
and corresponds to the Europe version.
There are, however, significantdifferencesto
petrol engine vehicles.
BMW. Nitrogen oxide emissions are
drastically reduced by the use of a reducing
agent that isinjected into the exhaustsystem
upstream of a special SCR catalytic
converter. Since the reducing agent is
carried in the vehicle, a supply facility, made
up of two reservoirs, is part of this system.
(digital diesel electronics)control unit that will
be used in thenext generation diesel engines
(N47, N57).
The preheater system also corresponds to
the N47/N57 engines.
that in the ECE variant of the X5 xDrive35d.
The gearbox itself has already been used in
the US version of the X5 4.8i, however, a
different torque converter is used for the
diesel model.
18
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8
Technical data
The following table compares the M57D30T2
US engine with petrol engines that are offered
for the same models.
To get an idea of the performance of the
M57D30T2 US engine, it is compared to
various petrol engines in the following full load
diagrams.
By comparing these two 3 litre engines it can
be clearly seen that, despite virtually identical
13 - M57D30T2 US engine
compared to
N52B30O1 engine
power output, the maximum torque of the
diesel is almost double as high.
20
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8
This enormous difference in maximum torque
is also apparent when comparing the
14 - M57D30T2 US engine
compared to
N54B30O0 engine
turbocharged 3 litre petrol engine that has a
considerably higher nominal power output.
21
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8
Even the 4.8 litre V8 engine cannot achieve
the maximum torque of the 3 litre diesel
engine.
However, the decisive factor is the low engine
speeds at which the diesel engine develops
15 - M57D30T2 US engine
compared to
N62B48O1 engine
this high torque. This means that more power
is available in this range. In terms of power
output, the diesel engine is superior to any of
these petrol engines up to an engine speed of
4000 rpm.
22
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9
System components.
Advanced Diesel.
Engine mechanical system
Only slight modifications have been made to
the engine mechanical system compared to
the Europe version.
Crankshaft and big-end bearings
Only lead-free crankcase and big-end
bearings are used in the M57D30T2 US
engine. This conforms to requirements
Crankcase
In contrast to the Europe version, the
M57D30T2 US engine has a larger
reinforcement panel on the underside of the
crankcase.
The reinforcement panel now covers four of
the main bearing blocks for the crankshaft.
Pistons
The piston pin has a greater offset than in the
Europe version. The offset of the piston pin
means that the piston pin is slightly off centre.
This provides acoustic advantages during
The modifications include:
• Crankcase
• Crankshaft and big-end bearings
• Pistons
• Crankcase breather.
relating to environmental protection and the
disposal of end-of-life vehicles.
In principle, the reinforcement panel serves to
enhance the stability of the crankcase.
However, the enlargement was realized solely
for acoustic reasons.
3 Never drive the vehicle without the
reinforcement panel. 1
changes in piston contact. The acoustic
advantages of increasing the offset are further
developed particularly at idle speed.
23
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9
Crankcase breather
The crankcase breather in the US version is
generally heated. In addition, operation of the
crankcase breather is OBD monitored (On
Board Diagnosis). This is because a leaking
system would produce emissions.
The only probable reason for a leak in the
system would be that the blow-by pipe is not
connected to the cylinder head cover. To
facilitate protection of this situation by the
OBD, the heating line isrouted via a connector
to the cylinder head cover (2). Essentially, this
connector serves only as a bridge so that
actuation of the heating system is looped
through. The plug connection is designed in
such a way that correct contact is made only
when the blow-by pipe has been connected
correctly to the cylinder head cover, i.e. the
contact for the heating system is not closed if
the blow-by pipe is not connected to the
cylinder head cover. OBD recognizes this
situation as a fault.
1 - Blow-by pipe
IndexExplanation
1Cylinder head cover
2Blow-by heater connector for OBD
monitoring
3Blow-by heater connector at wiring
harness
4Filtered air pipe
5Intake air from intake silencer
6Blow-by heater connector at blow-
by pipe
7Intake air to exhaust turbocharger
8Blow-by pipe
3 If the blow-by pipe is not connected to the
cylinder head correctly, the OBD will activate
the MIL (Malfunction Indicator Lamp). 1
24
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9
Air intake and exhaust system
The M57D30T2 US engine exhibits the
following special features in the air intake and
exhaust system:
• Electric swirl flaps
• Electric exhaust gas recirculation valve
(EGR valve)
• Low pressure EGR
• Turbo assembly adapted for low pressure
EGR.
2 - Air intake and exhaust system - M57D30T2 US engine
25
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9
IndexExplanationIndexExplanation
1M57D30T2 US engine18Oxidation catalytic converter and
2Intake silencer19Exhaust gas temperature sensor
3Hot-film air mass meter (HFM)20Oxygen sensor
4Compressor bypass valve21Wastegate
5Exhaust turbocharger, low pressure
EGR
10High pressure EGR valve27NOx sensor before SCR catalytic
11Throttle valve28Temperature sensor after diesel
12Charge air temperature sensor29Metering module (for SCR)
13Intercooler30Mixer (for SCR)
14Low pressure EGR valve with
positional feedback
15Temperature sensor,
low pressure EGR
16Low pressure EGR cooler33Digital Diesel Electronics (DDE)
17Exhaust gas temperature sensor
after oxidation catalytic converter
22Turbine control valve
23Exhaust pressure sensor after
24Swirl flap regulator
26Exhaust differential pressure sensor
31SCR catalytic converter
32NOx sensor after SCR catalytic
34Rear silencer
diesel particulate filter
before oxidation catalytic converter
exhaust manifold
converter
particulate filter
converter
26
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9
Air intake system
Intake air system
The intake air system differs on the E70 and
E90. Both vehicles draw in unfiltered air
behind the BMW kidney grille.
3 - Air intake system E70 and E90
IndexExplanationIndexExplanation
AAir intake system E703Intake silencer (air cleaner housing)
BAir intake system E904Hot-film air mass meter (HFM)
1Intake5Filtered air pipe
2Unfiltered air pipe6Blow-by pipe
On the E90, the intake silencer is located at
the front right oftheengine compartment fixed
to the vehicle. On the E70, the intake silencer
is fixed over the engine.
27
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9
Swirl flaps
The engine is equipped with the familiar swirl
flaps in thetangential port. A special feature on
the US engine is the electric actuating system
with positional feedback.
4 - Intake manifold with electric swirl flaps
IndexExplanationIndexExplanation
1Linkage for operating the swirl flaps5Swirl port
2Connection to throttle valve6Tangential port
3Intake manifold7Swirl flaps
4Electric motor
This system provides advantages in terms of
control, however, it is also a prerequisite for
meeting OBD requirements.
28
Page 35
Exhaust system
9
5 - E70 and E90 exhaust systems
29
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9
IndexExplanationIndexExplanation
AExhaust system E706SCR catalytic converter
BExhaust system E907NOx sensor after SCR catalytic
1Oxygen sensor and concealed
exhaust temperature sensor before
oxidation catalytic converter
2Exhaust gas temperature sensor
after oxidation catalytic converter
3Differential pressure sensor10Metering module
4NO
5Mixer
sensor before SCR catalytic
x
converter
8Rear silencer
9Exhaust gas temperature sensor
11Diesel particulate filter
converter
after diesel particulate filter
30
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9
Exhaust gas recirculation (EGR)
Exhaust gas recirculation is one of the
available options for reducing NOx emissions.
Adding exhaust gas to the intake air reduces
the oxygen in the combustion chamber, thus
resulting in a lower combustion temperature.
The EGR systems in the E70 and E90 differ.
Both vehicles are equipped with the familiar
EGR system. Due to its higher weight, the E70
additionally features low pressure EGR, used
for the first time at BMW.
Low pressure EGR
6 - Low pressure EGR
The known EGR system has been expanded
by the low pressure EGR on the E70. This
system offers advantages particularly at high
loads and engine speeds. This is why it is used
in the heavier E70 as it is often driven in the
higher load ranges.
The advantage is based on the fact that a
higher total mass of exhaust gas can be
recirculated. This is made possible for two
reasons:
• Lower exhaust gas temperature
The exhaust gas for the low pressure EGR
is tapped off at a point where a lower
temperature prevails than in the high
pressure EGR. Consequently, the exhaust
gas has a higher density thus enabling a
higher mass.
In addition, the exhaust gas is added to the
fresh intake air before the exhaust
turbocharger, i.e. before the intercooler,
where it is further cooled. The lower
temperature of the total gas enables a
higher EGR rate without raising the
temperature in the combustion chamber.
• Recirculation before the exhaust
turbocharger
Unlike in the high pressure EGR where the
exhaust gas is fed to the charge air already
compressed, in this system the exhaustgas
is added to the intake air before the exhaust
turbocharger. A lower pressure prevails in
this area under all operating conditions.
This makes it possible to recirculate a large
volume of exhaust gas even at higher
engine speed and load whereas this is
limited by the boost pressure in the high
pressure EGR.
31
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9
The following graphic shows the control of the
EGR system with low pressure EGR:
7 - Control of EGR system
IndexExplanationIndexExplanation
1No exhaust gas recirculation3High and low pressure EGR are
active
2Only high pressure EGR is active
As already mentioned, the low pressure EGR
has the greatest advantageat higher loads and
is therefore activated, as a function of the
characteristic map, only in this operating
mode. The low pressure EGR, however, is
never active on its own but rather always
operates together with thehighpressure EGR.
Added to this, it is only activated at a coolant
temperature of more than 55 °C. The low
pressure EGR valve is closed as from a certain
load level so that only the high pressure EGR
valve is active again. This means the EGR rate
is continuously reduced.
The low pressure EGR system is located on
the right-hand side on the engine directly next
to the diesel particulate filter and the low
pressure stage of the turbo assembly. The
exhaust gas is branched off directly after the
diesel particulate filter and fed to the intake air
before the compressor for the low pressure
stage.
33
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9
34
9 - Low pressure EGR intake
IndexExplanationIndexExplanation
1Low pressure EGR valve3Low pressure EGR port
2Compressor, low pressure stage4Unfiltered air intake
Page 41
9
The following graphic shows the components
of the low pressure EGR:
10 - LP EGR components
IndexExplanationIndexExplanation
1Temperature sensor,
low pressure EGR
2Low pressure EGR valve6Coolant return
3Connection for positional feedback7Low pressure EGR cooler
4Vacuum unit for
low pressure EGR valve
There is a fine meshed metal screen filter
located at the exhaust gas inlet from the diesel
particulate filter to the low pressure EGR
system. The purpose of this filter is to ensure
that no particles of the coating particularly in a
new diesel particulate filter can enter the low
pressure EGR system. Such particles would
5Coolant infeed
8Sheet metal gasket with filter
adversely affect the compressor blades of the
exhaust turbocharger.
3 The metal screen filter must be installed
when fitting the low pressure EGR cooler to
the diesel particulate filter otherwise there is a
risk of the turbocharger being damaged. 1
35
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9
High pressure EGRThe exhaust gas recirculation known to date is
referred to here as the high pressure EGR in
order to differentiate it from the low pressure
EGR.
Compared to the Europe version, the high
pressure EGR is equipped with the following
special features:
• Electric EGR valve with positional feedback
• Temperature sensor before high pressure
EGR valve
11 - High pressure EGR
• EGR cooler with bypass.
36
12 - High pressure EGR system
IndexExplanationIndexExplanation
1Coolant infeed5High pressure EGR cooler
2High pressure EGR valve6Vacuum unit of bypass valve for high
pressure EGR cooler
3Throttle valve7Coolant return
4Temperature sensor, high pressure
EGR
Page 43
9
The electric actuating system of the EGR
valve enables exact metering of the
recirculated exhaust gas quantity. In addition,
this quantity is no longer calculated based
solely on the signals from the hot-film air mass
meter and oxygen sensor but the following
signals are also used:
• Travel of high pressure EGR valve
• Temperature before high pressure EGR
valve
• Pressure difference between exhaust gas
pressure in the exhaust manifold and boost
pressure in the intake manifold.
Exhaust turbocharger
The US engine is equipped with the same
variable twin turbo as the Europe version,
however, the turbo assembly is modified due
to the low pressure EGR.
This enables even more exact control of the
EGR rate.
The EGR cooler serves the purpose of
increasing the efficiency of the EGR system.
However, reaching the operating temperature
as fast as possible has priority at low engine
temperatures. In this case, the EGR cooler can
be bypassed in order to heat up the
combustion chamber faster. For this purpose,
a bypass that diverts the coolant is integrated
in the EGR cooler. This bypass is actuated by
a flap which, in turn, is operated by a vacuum
unit. The bypass is either only in the "Open" or
"Closed" position.
On the one hand, the inlet for the low pressure
EGR is located on the compressor housing for
the low pressure stage. On the other hand, the
compressor wheels are nickel-coated to
protect them from the exhaust gas.
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9
Cooling system
The cooling system,is in part, vehicle-specific.
In principle, there are scarcely any differences
between the cooling systems on petrol and
diesel engines.
The two basic differences compared to petrol
engines are:
• No characteristic map thermostat
• EGR cooler.
The E70 andE90 differ with regard tothe EGR
cooler. Since the E70 is equipped with a low
pressure EGR system, it has a second EGR
cooler, the low pressure EGR cooler.
5High pressure EGR cooler13Expansion tank
6Thermostat14Gearbox oil cooler
7Coolant pump15Ventilation line
8Coolant temperature sensor16Electric fan
9Heating heat exchanger
10Duo-valve
11Auxiliary coolant pump
Engine oil-to-coolant heat exchanger
Gearbox oil-to-coolant heat
exchanger
40
Page 47
Fuel preparation system
9
15 - Fuel preparation system, M57D30T2 US engine
41
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9
IndexExplanationIndexExplanation
AFuel feed6Return line
BFuel return7Feed line
CFuel high pressure8Fuel temperature sensor
1Fuel rail pressure sensor9High-pressure line
2High-pressure line10Fuel rail
3Leakage oil line11Restrictor
4Piezo injector12High-pressure pump
5Fuel rail pressure control valve13Volume control valve
The fuel preparation system differs neither in
terms of design layout nor function from the
Europe version. However, some components
have been adapted to the different fuel
specification.
These components are:
• High-pressure pump
• Fuel rail
• Fuel injectors.
These adaptations are restricted to different
coatings and materials on the inside.
42
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9
Overview of fuel supply system
16 - E90 Diesel fuel supply system
43
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9
IndexExplanationIndexExplanation
1Fuel filler neck5Right-hand service opening
2Left-hand service opening6Filler vent
3Fuel return line7Electric fuel pump controller
4Fuel filter with heating system
Design
As for petrol engines, the fuel system is
vehicle-specific. There are, however, several
general and significant differences compared
to petrol engine vehicles.
These are:
• The system includes a fuel return line
• The breather system is significantly simpler
• There is no carbon canister (AKF) and no
fuel tank leakage diagnosis module (DMTL)
• There is no pressure regulator
• The fuel filter is not located in the fuel tank.
The design layout of the fuel supply systems
in the E70 and E90 are described in the
following.
In addition to delivering the fuel to the engine,
the fuel supply system also filters the fuel. The
fuel tank contains an additional venting
system.
The fuel tank is divided into two chambers
because of the space available in the vehicle.
The fuel supply system has two delivery units
that are accommodated in the right and left
fuel tank halves.
The fuel pump (3) with intake filter (2) is a part
of the right-hand delivery unit. The surge
chamber including a suction jet pump (10)
with pressure relief valve (11) and initial fill
valve (1) as well as a lever-type sensor (G)
complete this delivery unit.
45
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9
The suction jet pump (8), lever-type sensor
(G), leak prevention valve (7) and air inlet valve
(9) belong to the left-hand delivery unit.
E90 with diesel engine
A line leads from the filler vent valve (H) to the
filter (L). The fuel fillerpipe is connected to this
line via the non-return valve (K).
AFuel filler capEFuel tank
BPressure relief valveFService cap
CNon-return valveGLever-type sensor
DSurge chamber
A pressure relief valve (B) is integrated in the
fuel filler cap (A) to protect the fuel tank (E)
from excess pressure. A non-return flap (C) is
located at the end of the fuel filler neck. The
non-return flap prevents the fuel from sloshing
back into the fuel filler neck.
The components in the fuel tank can be
reached via the two service caps (F).
The fuel fill level can be determinedvia the two
lever-type sensors (G).
The surge chamber (D) ensures that the fuel
pump always has enough fuel available for
delivery.
47
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9
Fuel supply system
20 - Fuel supply system for E70 with diesel engine
In the event of the surge chamber being
completely empty, the initial filling valve (1)
ensures that fuel enters the surge chamber
while refuelling.
The fuel reaches the fuel pump (3) via the
intake filter (2), then continues through the
delivery line (5) to the fuel filter. The fuel pump
is located in the surge chamber. A pressure
relief valve (4) is integrated in the fuel pump to
prevent pressure inthe delivery line from rising
too high. As the engine switches off, the
delivery line is depressurized but cannot run
dry because, provided the system is not
leaking, no air is able to enter it. In addition,
after the fuel pump has switched off, the fuel
pressure/temperature sensor is checked for
plausibility.
Fuel that is required for lubrication and the
function of high pressure generation flows
back into the fuel tank via the return line (7).
The fuel coming from the return line is divided
into two lines downstream of the leak
prevention valve (7). The non-return valve
prevents the fuel tank from draining in the
event of damage to lines on the engine or
underbody. It also prevents the return line
from running dry while the engine is off.
One of the lines guides the fuel into the surge
chamber via a suction jet pump (10). The
suction jet pump transports the fuel from the
fuel tank into the surge chamber. If the fuel
delivery pressure in the return line increases
too much, the pressure relief valve (11) opens
and allows the fuel to flow directly into the
surge chamber.
An air inlet valve is used in the E70. The air
inlet valve (9) ensures that aircan enter the line
when the engine is off, preventing fuel from
flowing back from the right-hand half of the
fuel tank to the left.
Instead of the air inlet valve (9) a non-return
valve is used on the E90. The non-return valve
ensures that, while the engine is off, fuel from
the right-hand half of the fuel tank cannot flow
back into the left-hand half. The return system
remains completely filled with fuel.
A further line branches off into the left-hand
half of the fuel tank after the non-return valve
(7) and transports the fuel into the surge
chamber via the suction jet pump (8).
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9
Air supply and extraction
21 - Tank ventilation system for E70 with diesel engine
IndexExplanationIndexExplanation
HFiller vent valveKNon-return valve
IConnectionLFilter
JMaximum fill level
Fuel ventilation is ensured by means of the
filler vent valve (H).
The filler vent valve is located in the fuel tank
and uses the connection (I) to determine the
maximum fill level (J). The filler vent valve
contains afloat that buoys upwards on the fuel
when the vehicle is refuelled and blocks the
filler ventilation. The fuel rises in the fuel filler
and the fuel nozzle switches off.
A roll-over valve is also integrated in the filler
vent valve to block the ventilation line when a
certain angle of incline is reached and
prevents fuel from draining out if the vehicle
were to roll over.
The non-return valve (K) prevents fuel from
escaping via the ventilation when the vehicle is
refuelled. During operation, air can flow into
the fuel filler pipe and the fuel can flow from
the fuel filler pipe into the tank.
The filter (L) prevents dirt or insects from
entering the ventilation and blocking the line.
3 If the ventilation line does become
blocked, fuel consumption during operation
would cause negative pressure and the fuel
tank would be compressed and damaged. 1
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Components of the fuel supply system
Pressure relief valve in fuel filler cap
IndexExplanation
1Valve head
2Excess pressure spring
3Brace
4Bottom section of housing
5Pressure relief valve
6Sealed housing
22 - Pressure relief valve
The pressure relief valve ensures that, if there
is a problem with fuel tank ventilation, any
excess pressure that may form can escape
and the fuel tank is not damaged.
If excess pressure forms in the fuel tank, this
causes the valve head (1) and with it the entire
pressure relief valve (5) to be lifted off the
sealed housing (6). The excess pressure can
now escape into the atmosphere. The excess
pressure spring (2) determines the opening
pressure. The excess pressure spring uses a
defined pressure to push the pressure relief
valve onto the sealed housing and is
supported by the brace (3).
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9
Protection against incorrect refuelling
IndexExplanationIndexExplanation
1Housing5Torsion spring
2Locking lever6Rivet
3Tension spring7Hinged lever
4Flap8Ground strap
23 - Protection against
incorrect refuelling
24 - Protection against
incorrect refuelling
52
IndexExplanationIndexExplanation
∅ 21 mm Petrol fuel nozzle∅ 24 mm Diesel fuel nozzle
Page 59
9
The protection against incorrect refuelling
feature ensures that the fuel tank cannot be
filled with gasoline. As the previous graphic
shows, only a fuel nozzle with a diameter of
approximately 24 mm can fit. If the diameter is
approximately 21 mm, the flap (4) does not
open as the hinged lever (7) and the locking
lever (2) cannot be pushed apart.
If a diesel fuel nozzle is inserted, this pushes
the locking lever (2) and the hinged lever (7) at
the same time. The hinged lever is pushed
outwards against the tension spring (3) and
releases the flap (4). This is only possible,
however, if the hinged lever cannot move
freely and is also locked in position by the fuel
nozzle.
3 To open the protection against incorrect
refuelling feature in the workshop, a special
tool is required. 1
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9
Fuel pump
Today's diesel vehicles are fitted with electric
fuel pumps only. The electric fuel pump is
designed to deliver a sufficient amount of fuel
to lubricate and cool the injectors and the
high-pressure pump and to satisfy the
maximum fuel consumption of the engine. It
has to deliver the fuel at a defined pressure.
That means that when the engine is idling or
running at medium power, the fuel pump
delivers several times more than the amount
of fuel required. The fuel pump delivers
approximately three or four times the volume
of maximum possible fuel consumption.
The electric fuel pump is located in the fuel
tank. There it is well protected against
corrosion and the pump noise is adequately
soundproofed.
The fuel pump on BMW diesel engines may
either be a gear pump, a roller-cell pump or a
screw-spindle pump. The following fuel
pumps are used on USA vehicles:
VehicleFuel pump
E70Screw-spindle pump
E90Gear pump
The operating principle of each of these types
of pump is described below. The pump itself is
driven by the drive shaft (2) of the electric
motor (3). The electric motor is controlled by
the electrical connection (6) and sliding
contacts (7).
Passing first through the intake filter and then
the remainder of the intake section (9), the fuel
enters the impeller (1). The fuel is pumped
through pressure chamber (8) on the electric
motor, past the pressure connection (5) and
onwards to the fuel filter and engine.
If the fuel delivery pressure increases to an
impermissible value, the pressure relief valve
(4) opens and allows the fuel to flow into the
surge chamber.
Control
In principle, there are three different types of
fuel pump control:
• Unregulated:
The fuel pump operates with "ignition ON".
If the engine is not started, the fuel pump
switches off again after a defined period. If
the engine is running, the fuel pump
operates at maximum output and speed.
The fuel is switched off with "engine OFF".
• Speed-regulated:
The fuel pump operates with "ignition ON".
If the engine is not started, the fuel pump
switches off again after a defined period.
The fuel pump is controlled by an
interposed control unit (fuel pump
controller) in response to a request signal
from the DDE. The fuel pump controller
monitors and regulates the pump speed. If
the engine is switched off, so too is the fuel
pump.
• Pressure-regulated:
The fuel pump operates with "ignition ON".
If the engine is not started, the fuel is
switched off at a specific pressure. When
the engine is running, the fuel pump is
regulated on-demand by the interposed
fuel pump controller in response to a load
signal from the DDE in order to ensure a
uniform fuel pressure at the inlet to the
high-pressure pump.
Both speed regulation andpressureregulation
have improved fuel economy, although it has
been possible to improve fuel economy
further still with pressure regulation. Other
positive side effects include an increase in the
fuel pump's service life, an unloading of the
vehicle electrical system and a reduction in
fuel pump noise.
VehicleControl
E70Pressure control
E90Speed control
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Gear pump
The type of gear pump used is a rotor pump.
The rotor pump comprises an outer rotor (1)
with teeth on the inside, and an inner rotor (4)
with teeth on the outside. The inner rotor is
driven by the drive shaft (5) of the electric
motor. The outer rotor is propelled by the
teeth of the inner rotor and thus turns inside
the pump housing.
The inner rotor has one tooth fewer than the
outer rotor, which means that, with each
revolution, fuel is carried into the next tooth
gap of the outer rotor.
During the rotary motion, the spaces on the
intake side enlarge, while those on the
pressure side become proportionately smaller.
The fuel isfed into the rotorpump through two
grooves in the housing, one on the intake side
and one on the pressure side. Together with
the tooth gaps, these grooves form the intake
section (6) and pressure section (3).
26 - Gear pump/rotor pump
IndexExplanation
1Outer rotor
2Fuel delivery to the engine
3Pressure section
4Inner rotor
5Drive shaft
6Intake section
7Fuel from the fuel tank
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Screw-spindle pump
With the screw-spindle pump, two screw
spindles intermesh in such a way that the
flanks form a seal with each other and the
housing. In the displacement chambers
between the housing and the spindles, the
fuel is pushed towards the pressure side with
practically no pulsation.
In this way, the screw spindles pump fuel away
from the fuel tank (5). The fuel is then fed to
the engine (3) through the pump housing and
the fuel delivery line.
27 - Screw-spindle pump
IndexExplanation
1Drive shaft screw spindle
2Gearwheel
3Fuel delivery to the engine
4Screw spindle
5Fuel from the fuel tank
57
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Fuel filter
The fuel filter with heater illustrated here was
used in vehicle models with diesel engine and
distributor injection pump. Later models with
diesel engine and common rail system are
equipped with the following fuel filters.
28 - Fuel filter with heater (later vehicle models)
3 BMW recommends the use of parts and
accessories for the vehicle that have been
approved by BMW for this purpose. These
parts and accessories have been tested by
BMW for their functional safety and
compatibility in BMW vehicles. BMW accepts
product responsibility for them. However,
BMW cannot accept any liability for nonapproved parts or accessories. 1
The job of the fuel filter is to protect the fuel
system against dirt contamination. The highpressure pump and injectors in particular are
very sensitive and can be damaged by even
the tiniest amounts of dirt. The fuel delivered
to the engine is always fed through the fuel
filter. Contaminants are trapped by a paperlike material. The fuel filter is subject to a
replacement interval.
IndexExplanation
1Fuel filter heater connection
2Inlet into the fuel filter heating
3Locking clamp
4Fuel filter
5Connection between fuel line and
high-pressure pump
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Fuel filter heater
The fuel filter heater is attached to the fuel
filter housing and fixed with a locking clamp.
The fuel flows through the fuel filter heating
into the fuel filter.
Since winter-grade diesel fuel remains thin
even at low temperatures, the fuel filter heater
is not normally active when winter-grade
diesel fuel is used. In order to save energy, the
fuel filter heater is only switched on when the
diesel actually becomes viscous due to low
temperatures.
There are two different control systems
depending on whether the fuel supply system
is speed-controlled or pressure-controlled.
Speed-controlled system
The fuel filter heater is not controlled by the
DDE. A pressure switch and a temperature
sensor are located in the fuel filter housing.
The fuel filter heater is switched on when both
of the following conditions are fulfilled:
• Temperature drops below a defined value
• A defined fuel delivery pressure is
exceeded due to cold, viscous fuel.
If the filter is clogged, a corresponding signal is
sent via a diagnosis line to the DDE. This is the
case when, despite a sufficiently high
temperature, the fuel pressure upstream of
the filter does not drop.
Pressure-controlled system
The fuel filter heater is actuated by the DDE. A
combined fuel pressure and temperature
sensor upstream of the high pressure pump is
used.
The fuel filter heater is switched on when both
of the following conditions are fulfilled:
• Temperature drops below a defined value
• The required fuel pressure is not reached
despite increased power intake of the
electric fuel pump.
The DDE recognizes a clogged filter when the
target pressure upstream of the high pressure
pump is not reached despite asufficiently high
fuel temperature and high power intake of the
electric fuel pump.
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Overview of selective catalytic reduction
Selective catalytic reduction is a system for
reducing nitrogen oxides (NOx) in the exhaust
gas. For this purpose, a reducing agent (ureawater solution) is injected into exhaust gas
downstream of the diesel particulate filter.
The nitrogen oxide reduction reaction then
takes place in the SCR catalytic converter.
The urea-water solution is carried in two
reservoirs in the vehicle. The quantity is
measured out such that it is sufficient for one
oil change interval.
The following graphic shows a simplifiedrepresentation of the system:
60
29 - Simplified representation of SCR system
Page 67
9
IndexExplanationIndexExplanation
1Passive reservoir10Pump
2Level sensors11Filter
3Filler pipe, passive reservoir12Transfer line
4Metering line13Metering module
5Metering line heater14Level sensor
6Pump15Filler pipe, active reservoir
7Function unit16Exhaust system
8Heater in active reservoir17SCR catalytic converter
9Active reservoir
The reason for using two reservoirs is that the
urea-water solution freezes at a temperature
of -11 °C. Forthis reason, the smaller reservoir
is heated but the larger reservoir not. In this
way, the entire volume of the urea-water
solution need not be heated, thus saving
energy. The amount is sufficient, however, to
cover large distances.
The small, heated reservoir is referred to as
the active reservoir. A pump conveys the ureawater solution from this reservoir to the
metering module. This line is also heated.
The larger, unheated reservoir is the passive
reservoir. A pump regularly transfers the ureawater solution from the passive reservoir to
the active reservoir.
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Installation locations in the E70
62
30 - Installations locations, E70 SCR system
Page 69
9
IndexExplanationIndexExplanation
1Active reservoir8Passive reservoir
2Delivery module9Metering module
3Filler for active reservoir10Exhaust gas temperature sensor
after diesel particulate filter
4Transfer unit11NOx sensor before SCR catalytic
converter
5Filter12Filler for passive reservoir
6SCR catalytic converter13Oxidation catalytic converter and
diesel particulate filter
7NOx sensor after SCR catalytic
converter
On the E70, the active reservoir, including the
delivery unit, is located on the right-hand side
directly behind the front bumper panel. The
passive reservoir is located on the left in the
underbody, approximately under the driver's
seat. The transfer unit is installed on the right
in theunderbody. Both fillers are located in the
engine compartment.
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Installation locations in the E90
64
31 - Installations locations, E90 SCR system
Page 71
9
IndexExplanationIndexExplanation
1Active reservoir8Passive reservoir
2Delivery module9Metering module
3Filler for active reservoir10Exhaust gas temperature sensor
after diesel particulate filter
4Transfer unit11NOx sensor before SCR catalytic
converter
5Filter12Filler for passive reservoir
6SCR catalytic converter13Oxidation catalytic converter and
diesel particulate filter
7NOx sensor after SCR catalytic
converter
On the E90,both the active reservoir aswell as
the passive reservoir are located under the
luggage compartment floor with the active
reservoir being the lowermost of both. The
fillers are located on the left-hand side behind
the rear wheel where they are accessible
through an opening in the bumper panel. The
fillers are arranged in the same way as the
reservoirs, i.e. the lowermost is the filler for the
active reservoir. The transfer unit and the filter
are located behind the filler.
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9
Detailed system overview
66
32 - SCR system overview
Page 73
9
IndexExplanationIndexExplanation
1Operating vent19Filter
2Passive reservoir20Metering line heater
3Level sensors21Metering line
4Filler vent22Operating vent
5Filler pipe23Temperature sensor
6Transfer line24Level sensor
7Delivery module25Intake line heater
8Delivery module heater26Filter
9Delivery pump27Active reservoir
10Reversing valve28Heating element in function unit
11Filter29Function unit
12Pressure sensor30Filler pipe
13Filter31Metering module
14Restrictor32NOx sensor before SCR catalytic
converter
15Extractor connections33Exhaust gas temperature sensor
after diesel particulate filter
16Filler vent34SCR catalytic converter
17Non-return valve35NOx sensor after SCR catalytic
converter
18Transfer pump
67
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9
E70 System circuit diagram
68
33 - E70 SCR system circuit diagram
Page 75
9
IndexExplanationIndexExplanation
1Heater module10Exhaust gas temperature sensor
after diesel particulate filter
2Delivery module with delivery pump,
reversing valve, pressure sensor and
heater
3Function unit with level sensor in
active reservoir, temperature sensor
and heater
4Active reservoir13Passive reservoir
5Metering line heater14Level sensors in passive reservoir
6Digital Diesel Electronics (DDE)15Evaluator, level sensors in passive
7NOx sensor after SCR catalytic
converter
8NO
9Metering module18Evaluator, level sensor in active
sensor before SCR catalytic
x
converter
11Transfer pump
12Power distributor, battery
reservoir
16DDE main relay
17Power distributor, junction box
reservoir
69
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9
E90 System circuit diagram
70
34 - E90 SCR system circuit diagram
Page 77
9
IndexExplanationIndexExplanation
1DDE main relay11Transfer pump
2Digital Diesel Electronics (DDE)12Evaluator, level sensor in active
reservoir
3SCR relay13Function unit with level sensor in
active reservoir, temperature sensor
and heater
4Power distributor, junction box14Active reservoir
5Exhaust gas temperature sensor
after diesel particulate filter
6Metering module16Heater module
7Power distributor, battery17NOx sensor after SCR catalytic
8Passive reservoir18NOx sensor before SCR catalytic
9Level sensors in passive reservoir19SCR load relay
10Evaluator, level sensors in passive
reservoir
15Delivery module with delivery pump,
reversing valve, pressure sensor and
heater
converter
converter
20Metering line heater
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Functions of selective catalytic reduction system
Selective catalytic reduction is currently the
most effective system for reducing nitrogen
oxides (NOx). During operation, it achieves an
efficiency of almost 100 % and approx. 90 %
over the entire vehicle operating range. The
difference is attributed to the time the system
35 - SCR functions
IndexExplanationIndexExplanation
1NOx sensor before SCR catalytic
converter
2Metering module4Temperature sensor after diesel
requires until it is fully operative after a cold
start.
This system carries a reducing agent, ureawater solution, in the vehicle.
3NOx sensor after SCR catalytic
converter
particulate filter
The urea-water solution is injected into the
exhaust pipe by the metering module
upstream of the SCR catalytic converter. The
DDE calculates the quantity that needs to be
injected. The nitrogen oxide content in the
exhaust gas is determined by the NOxsensor
before the SCR catalytic converter.
Corresponding to this value, the exact quantity
of the urea-water solution required to fully
reduce the nitrogen oxides is injected.
The urea-water solution converts to ammonia
in the exhaust pipe. In the SCR catalytic
converter, the ammonia reacts with the
nitrogen oxides to produce nitrogen (N2) and
water (H2O).
A further NOx sensor that monitors this
function is located downstream of the SCR
catalytic converter.
A temperaturesensor in the exhaust pipe after
the diesel particulate filter (i.e. before the SCR
catalytic converter) and the metering module
also influences this function. This is because
injection of the urea-water solution only
begins at a minimum temperature of 200 °C.
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Chemical reaction
The task of the SCR system is to substantially
reduce the nitrogen oxides (NOx) in the
exhaust gas. Nitrogen oxides occur in two
different forms:
• Nitrogen monoxide (NO)
• Nitrogen dioxide (NO2).
36 - Nitrogen oxides
Ammonia (NH3) is used for the purpose of
reducing the nitrogen oxides in a special
catalytic converter.
38 - Urea-water solution
The urea-water solution is injected by the
metering system into the exhaust system
downstream of the diesel particulate filter. The
required quantity must be metered exactly as
otherwise nitrogen oxides or ammonia would
emerge at the end. The following description
of the chemical processes explains why this is
the case.
37 - Ammonia
The ammonia is supplied in the form of a ureawater solution.
The conversion of urea into ammonia takes
place in two stages.
Conversion of the urea-water solution
The uniform distribution of the urea-water
solution in the exhaust gas and the conversion
to ammonia take place in the exhaust pipe
upstream of the SCR catalytic converter.
Initially, the urea ((NH2)2CO) dissolved in the
urea-water solution is released.
39 - Release of urea from the
urea-water solution
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Thermolysis
Explanation:During thermolysis, the urea-water solution is split into two products
as the result of heating.
Initial product:Urea ((NH2)2CO)
Result:Ammonia (NH3)
Isocyanic acid (HNCO)
Chemical formula:(NH2)2CO → NH3 + HNCO
40 - Thermolysis: Urea converts to ammonia and isocyanic acid
This means, only a part of the urea-water
solution is converted into ammonia during
thermolysis. The remainder, which is in the
Hydrolysis
Explanation:The isocyanic acid that was produced during thermolysis is converted
into ammonia and carbon dioxide (CO2) by the addition of water in the
Carbon dioxide (CO2)
Chemical formula:HNCO + H2O → NH3 + CO
41 - Hydrolysis: Isocyanic acid reacts with water to form ammonia and carbon dioxide
form of isocyanic acid, is converted in a
second step.
2
74
The water required for this purpose is also
provided by the urea-water solution.
Therefore, following hydrolysis, all the urea is
converted into ammonia and carbon dioxide.
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NOx reduction
Nitrogen oxides are converted into harmless
nitrogen and water in the SCR catalytic
converter.
42 - Nitrogen and water
Reduction
Explanation:The catalytic converter serves as a "docking" mechanism for the
ammonia molecules. The nitrogen oxide molecules meet the
ammonia molecules and the reaction starts and energy is released.
This applies to NO in the same way as to NO2.
Initial products:Ammonia (NH3)
Nitrogen monoxide (NO)
Nitrogen dioxide (NO2)
Oxygen (O2)
Result:Nitrogen (N2)
Water (H2O)
Chemical formulae:NO + NO2 + 2NH3→ 2N2 + 3H2O
4NO + O2 + 4NH3→ 4N2 + 6H2O
6NO2 + 8NH3→ 7N2 + 12H2O
43 - NOx reduction: Nitrogen oxides react with ammonia to form nitrogen and water
It can be seen that each individual atom has
found its place again at the end of the process,
i.e. exactly the same elements are on the left
as on the right. This takes place only when the
ratio of the urea-water solution to nitrogen
oxides is correct. Nitrogen oxides would
emerge if too little urea-water solution were
injected. By the same token, ammonia would
emerge if too much urea-water solution were
injected, resulting in unpleasant odour and
possible damage to the environment.
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SCR control
The SCR control is integrated in the digital
diesel electronics (DDE). The SCR control is
divided into the metering system control and
the metering strategy.
44 -
IndexExplanationIndexExplanation
1Digital diesel electronics DDE710Pressure sensor
2SCR control11Temperature sensor in active
reservoir
3Metering system control12Outside temperature sensor
4Metering strategy13Level sensor in active reservoir
5Injection pump14Level sensor in passive reservoir
6Transfer pump15NOx sensor before SCR catalytic
converter
7Metering module16NOx sensor after SCR catalytic
converter
8Heater17Exhaust temperature sensor
9Reversing valve
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Metering strategy
The metering strategy is an integral part of the
SCR control that calculates how much areawater solution is to be injected at what time.
During normal operation, the signal from the
NOx sensor before the SCR catalytic
converter is used for the purpose of
calculating the quantity. This sensor
determines the quantity of nitrogen oxide in
the exhaust gas and sends the corresponding
value to the DDE.
However, the NOx sensor must reach its
operating temperature before it can start
measuring. Depending on the temperature,
this can take up to 15 minutes. Until then the
DDE uses a substitute value to determine the
amount of nitrogen oxide in the exhaust gas.
A second NOx sensor is installed after the
SCR catalytic converter for the purpose of
monitoring the system. It measures whether
there are still nitrogen oxides in the exhaust
gas. If so the injected quantity of the ureawater solution is correspondingly adapted.
The NOxsensor, however, measures not only
nitrogen oxides but also ammonia but cannot
distinguish between them.
If too much urea-water solution is injected,
although the nitrogen oxides are completely
reduced so-called "ammonia slip" occurs, i.e.
ammonia emerges from the SCR catalytic
converter. This in turn causes a rise in the
value measured by the NOx sensor. The aim,
therefore, is to achieve a minimum of the
sensor value.
45 - Nitrogen and ammonia emission diagram
IndexExplanation
AValue output by NOx sensor
BInjected quantity of urea-water
solution
1Too little urea-water solution
injected
2Correct quantity of little urea-water
solution injected
3Too much urea-water solution
injected
This, however, is a long-term adaptation and
not a short-term control process as the SCR
catalytic converter performs a storage function
for ammonia.
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Metering system control
The metering system control could be
considered as the executing part. It carries out
the requirements setby the metering strategy.
This includes both the metering, i.e. injection
as well as the supply of the urea-water
solution.
The tasks of the metering system control
during normal operation are listed in the
following:
Metering of the urea-water solution:
• Implementation of the required target
quantity of urea-water solution
• Feedback of the implemented actual
Supplying urea-water solution:
• Preparation of meteringprocess(filling lines
• Emptying lines during afterrunning
• Heater actuation.
In addition, the metering system control
recognizes faults, implausible conditions or
critical situations and initiates corresponding
measures.
Metering of the urea-water solution
The metering strategy determines the
quantity of urea-water solution to be injected.
The metering system control executes this
request. A part of the function is metering
actuation that determines the actual opening
of the metering valve.
Depending on the engine load, the metering
valve injects at a rate of 0.5 Hz to 3.3 Hz.
The metering actuation facility calculates the
following factors in order to inject the correct
quantity:
• The duty factor of the actuator of the
metering valve in order to determine the
injection duration
• Actuation delay to compensate for the
sluggishness of the metering valve.
The signal from the pressure sensor in the
metering line is taken into account to ensure
an accurate calculation; the pressure,
however, should remain at a constant 5 bar.
The metering system control also calculates
the quantity actually metered and signals this
value back to the metering strategy.
The metering quantity is also determined over
a longer period of time. This long-term
calculation is reset during refuelling or can be
reset by the BMW diagnosis system.
quantity of urea-water solution.
and pressure built-up)undercorresponding
ambient conditions (temperature)
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Supplying urea-water solution
A supply of a urea-water solution is required
for the selective catalytic reduction process. It
is necessary to store this medium in the
vehicle and to make it available rapidly under
all operating conditions. In this case 'making
available' means that the urea-water solution
is applied at a defined pressure at the
metering valve.
Various functions that are described in the
following are required to carry out this task.
Heater
The systemmust be heated as the urea-water
solution freezes at a temperature of -11 °C.
The heating system performs following tasks:
• To monitor the temperature in the active
reservoir and the ambient temperature
• To thaw a sufficient quantity of urea-water
solution and the components required for
metering the solution during system startup
• To prevent the relevant components
freezing during operation
• To monitor the components of the heating
system.
The following components are heated:
• Surge chamber in active reservoir
• Intake line in active reservoir
• Delivery module (pump, filter, reversing
valve)
• Metering line (from active reservoir to
metering module).
The heating systems for the metering line and
delivery module are controlled dependent on
the ambient temperature.
The heater in the active reservoir is controlled
as a function of the temperature in the active
reservoir.
The heating control is additionallygovernedby
the following conditions:
Temperature in active reservoir and ambient temperature are the same
Condition 1 Condition 2 Condition 3 Condition 4
Ambient temperature and
temperature in active reservoir
Metering line heaterNot activeNot activeActiveActive
Active reservoir heaterNot activeActiveActiveActive
Metering standbyEstablishedEstablishedEstablishedDelayed
> -4 °C< -4 °C< -5 °C< -9 °C
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Metering standby is delayed at a temperature
below -9 °C in the active reservoir, i.e. a
defined waiting period is allowed to elapse
until an attempt to build up pressure begins.
This time is constant from -9 °Cto -16.5 °Cas
it is not possible to determine to what extent
the urea-water solution is frozen. At
temperatures below -16.5 °C, the heating
time is extended until an attempt to build up
the pressure is made.
Heating the metering line generally takes
place much faster.Therefore, the temperature
in the active reservoir is the decisive factor for
the period of time until an attempt to build up
the pressure is undertaken. However, it is
possible that the heating time for the metering
line is longer at ambient temperature
considerably lower than the temperatureinthe
active reservoir. In this case, the ambient
temperature is taken for the delay in metering
standby.
The following graphic shows the delay as a
function of the temperature sensor signals.
46 - Diagram - metering
standby delay times
IndexExplanationIndexExplanation
ADelay as a function of temperature in
active reservoir
t [s]Delay time in secondsT [°C]Temperature in degrees Celsius
The graphic shows that, with the same
temperature signals, the delay time relating to
the temperature in the active reservoir is
longer than the delay caused by the ambient
temperature.
Only the times at temperatures below -9 °C
are relevant as they are shorter than 3 minutes
at temperatures above -9 °C. 3 minutes is the
time that the entire system requires to
establish metering standby (e.g. also taking
BDelay as a function of ambient
temperature
into account the temperature in the SCR
catalytic converter). This is also the time that is
approved by the EPA (Environmental
Protection Agency) as the preliminary period
under all operating conditions. This time is
extended significantly at very low
temperatures.
The following example shows how the delay
time up to metering standby is derived at low
temperatures.
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Example: Ambient temperature: -30 °C,
temperature in active reservoir: -12 °C
The vehicle was driven for a longer period of
time at very low ambient temperatures of 30 °C. The heater in the active reservoir has
thawed the urea-water solution. The vehicle is
now parked for a short period of time (e.g. 30
minutes). When restarted, the temperature in
the active reservoir is -12 °C.
The delay time that is initiated by the
temperature in the active reservoir is approx.
18 minutes while the delay time initiated by
the ambient temperature is 25 minutes. Since
the delay time initiated by the ambient
temperature is longer, this will give rise to a
longer delay.
Now another condition comes into play. Only
the end of the delay caused by the
temperature in the active reservoir can enable
metering. This means:
• The delay time initiated by the temperature
in the active reservoir will have elapsed after
18 minutes. No enable is yet provided by
the second delay caused by the ambient
temperature. A second cycle of 18 minutes
now begins.
• The delay time initiated by the ambient
temperature will elapse after 25 minutes
and will send its enable signal. However,
this delay cannot enable metering.
• The second cycle of the delay time caused
by the temperature in the active reservoir
will have elapsed after 36 minutes. Since
the enable from the delay caused by the
ambient temperature is now applied,
metering will be enabled.
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Transfer pumping
So-called transfer pumping is required since
two reservoirs are used for storing the ureawater solution. The term transfer pumping
47 - Transfer pumping
relates to pumping the urea-water solution
from the passive reservoir into the active
reservoir.
The following conditions must be met for
transfer pumping:
• There is aurea-water solution in the passive
reservoir
• The ambient temperature is above a
minimum value of -5 °C for at least 10
minutes
• A defined quantity (300 ml) was used up in
the active reservoir or the reserve level in
the active reservoir was reached.
The solution is then pumped for a certain time
in order to refill the active reservoir. The
transfer pumping procedure is terminated if
the "full" level is reached before the time has
elapsed.
If the passive reservoir was refilled, transfer
pumping will only take place after a quantity of
approx. 3 l has been used up in the active
reservoir. The entire quantity is then pumped
over. The system then waits again until a
quantity of approx. 3 l has been used up in the
active reservoir before again pumping the
entire quantity while simultaneously starting
the incorrect refilling detection function. This
function determines whether the system has
been filled with the wrong medium as it is
present in high concentration in the active
reservoir.
Transfer pumping does not take place in the
event of a fault in the level sensor system.
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Delivery
The urea-water solution is delivered from the
active reservoir to the metering module. This
task is performed by a pump that is integrated
in the delivery unit. The delivery unit
additionally contains:
The pump is actuated by a pulse-width
modulated signal (PWM signal) from the DDE.
The PWM signal provides a speed
specification for the purpose of establishing
the system pressure. The value for the speed
specification is calculated by the DDE based
on the signal from the pressure sensor.
When the system starts up, the pump is
actuated with a defined PWM signal and the
line to the metering module is filled. This is
followed by pressure build-up. Only then does
pressure control take place.
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When the metering line is filled, the opened
metering valve allows a small quantity of the
urea-water solution to be injected into the
exhaust system.
During pressure control, i.e. during normal
operation with metering, the pump is actuated
in such a way that a pressure of 5 baris applied
in the metering line. Only a small part of the
urea-water solution delivered by the pump is
actually injected. The majorityof the solution is
transferred via a throttle back into the active
reservoir. This means, the delivery pressure is
determined by the pump speed together with
the throttle cross section.
The solution is injected four times per second.
The quantity is determined by the opening
time and stroke of the metering valve.
However, the quantity is so low that there is no
noticeable drop in pressure in the metering
line.
Evacuating
After turning off theengine, the reversing valve
switches to reverse the delivery direction of
the pump, thus evacuating the metering line
and metering module.
Evacuation also takes place if the system has
to be shut down due to a fault or if the
minimum temperature in the active reservoir
can no longer be maintained.
This is necessary to ensure no urea-water
solution remains in the metering line or
metering module as it can freeze.
The metering valve is opened during
evacuation.
Level measurement
There are level sensors both in the active as
well as in the passive reservoir. However,
these sensors are not continuous sensors as
in the fuel system for example. They can
determine only a specific point, to which a
defined quantity of urea-water solution in the
reservoir is assigned.
Two separate level sensors are fitted in the
passive reservoir, one for "full" and one for
"empty". The signals from the level sensors
are not sent directly to the DDE but rather to
an evaluator.
The active reservoir contains one level sensor
that has various measuring points:
• Full
• Warning
• Empty.
Also in this case, there is an evaluator installed
between the sensors and the DDE, which
fulfils the same tasks as for the passive
reservoir.
This evaluator sends a plausible level signal to
the DDE. It recognizes changes in the fill level
caused, for example, by driving uphill/downhill
or sloshing of the liquid as opposed to an
actual change in the liquid level in the
reservoir. Low level isthereforesignalled when
the corresponding sensor isnolonger covered
by the urea-water solution for a defined period
of time. Once the level drops below this value,
it can no longer be reached during normal
operation. This means, the liquid sloshing on
the sensor or driving uphill/downhill is no
longer interpreted as a higher liquid level.
50 - Example: Level signal OK
IndexExplanation
1Measuring point "Full"
2Measuring point "Warning"
3Measuring point "Empty"
4Reference
5Level
The level measurement system must also
recognize when the active and passive
reservoirs are refilled. This is achieved by
comparing the current level with the value last
stored.
The level sensor signal after refilling
corresponds to the signal while driving uphill.
To avoid possible confusion, the refilling
recognition function is limited to a certain
period of time after starting the engine and
driving off - as it can be assumed that refilling
will only take place while the vehicle is
stationary.
A certain vehicle speed must be exceeded to
ensure that sloshing occurs, thus providing a
clear indication that the system has been
refilled.
Refilling the system while the engine is
running can also be detected but with
modified logic. The signals sent by the
sensors while the vehicle is stationary are also
used for this purpose. The vehicle must be
stationary for a defined minimum period in
order to make the filling plausible.
When the urea-water solution is frozen, a level
sensor will show the same value as when it is
not wetted/covered by the solution. A frozen
reservoir is therefore shown as empty. For this
reason, the following sensor signals are used
for measuring the level:
• Ambient temperature
• Temperature in active reservoir
• Heater enable.
Level calculation
This function calculates the quantity of ureawater solution remaining in the active
reservoir. The calculation is calibrated
together with the level measurement.
Every time the level drops below a level sensor
the corresponding amount of urea-water
solution in the reservoir is stored. The amount
of urea-water solution actually injected is then
subtracted from this value while the pumped
quantity is added.
This makes it possible to determine the level
more precisely than that would be possible by
simple measurement. In addition, thelevel can
still be determined in the event of one of the
level sensors failing.
Since it is possible that refilling is not
recognized, the calculation is continued only
until the level ought to drop below the next
lower sensor.
Example:
Once the level drops below the "full" level
sensor, for example, from now on the quantity
of used and repumped urea-water solution is
taken into account and the actual level below
"full" calculated. Normally, the level thendrops
below the next lower level sensor at the same
time as determined by the level calculation. An
adjustment takes place at this point and the
calculation is restarted.
If, however, a quantity of urea-water solution is
refilled without it being detected, the actual
level will be higher than the calculated level.
The level calculation is stopped if it calculates
that the level ought to have dropped below the
next level sensor but the level sensor is still
wetted/covered.
By way of exception, a defective level sensor
can cause the calculation to continue until the
reservoir is empty.
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SCR system modes
When the ignition is switched on, the SCR
control undergoes a logical sequence of
modes in the DDE. There are conditions that
initiate the change from one mode to the
other. The following graphic shows the
sequence of modes which are subsequently
described.
51 - Sequence of modes in SCR control
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INIT (SCR initialization)
The control unit is switched on (terminal 15
ON) and the SCR system is initialized.
STANDBY (SCR not active)
STANDBY mode is assumed either after
initialization or in the case of fault.
AFTERRUN mode is assumed if terminal 15 is
switched off in this state or a fault occurs.
NOPRESSURECONTROL (waiting for
enable for pressure control)
NOPRESSURECONTROL mode is assumed
when no faults occur in the system. In this
mode, the system is waiting for the pressure
control enable that is provided by the following
sensor signals:
• Temperature in catalytic converter
• Temperature in active reservoir
• Ambient temperature
• Engine status (engine running).
The system also remains in
NOPRESSURECONTROL mode for a
minimum period of time so that a plausibility
check of the pressure sensor can be
performed.
PRESSURECONTROL mode is assumed
once the enable is finally given.
STANDBY mode is assumed if terminal 15 is
switched off or a fault occurs in
NOPRESSURECONTROL mode.
PRESSURECONTROL (SCR system
running)
PRESSURECONTROL mode is the normal
operating status of the SCR system and has
four submodes.
PRESSURECONTROL mode is maintained
until terminal 15 is switched off. A change to
PRESSUREREDUCTION mode then takes
place.
A change to PRESSUREREDUCTION mode
also takes place if a fault occurs in the system.
The four submodes of
PRESSURECONTROL are described in the
following:
• REFILL
The delivery module, metering line and the
metering module are filled when REFILL
mode is assumed. The pump is actuated
and the metering valve opened by a defined
value. The fill level is calculated.
The mode changes to
PRESSUREBUILDUP when the required fill
level is reached or a defined pressure
increase is detected.
PRESSUREREDUCTION mode is
assumed if terminal 15 is switched off or a
fault occurs in the system.
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• PRESSUREBUILDUP
In this mode, the pressure is built up to a
certain value. For this purpose, the pump is
actuated while the metering valve is closed.
If the pressure is built up within a certain
time, the system switches to the next mode
of METERINGCONTROL. If the required
pressure built-up is not achieved after the
defined period of time has elapsed, a status
loop is initiated,andVENTILATION mode is
assumed.
If the pressure cannot be built up after a
defined number of attempts, the system
signals a fault and assumes
PRESSUREREDUCTION mode.
PRESSUREREDUCTION mode is also
assumed when terminal 15 is switched off
or another fault occurs in the system.
• VENTILATION
If the pressure could not be increased
beyond a certain value in
PRESSUREBUILDUP mode, it is assumed
that there is still air in the pressure line.
The metering valve is opened for a defined
period of time to allow this air to escape.
This status is exited after this time has
elapsed and the system returns to
PRESSUREBUILDUP mode. The loop
between PRESSUREBUILDUP and
VENTILATION varies corresponding to the
condition of thereducing agent. The reason
for this is that a different level is established
after REFILL depending on the ambient
conditions. Repeating the ventilation
function will ensure that the pressure line is
completely filled with reducing agent.
PRESSUREREDUCTION mode is
assumed if terminal 15 is switched off or a
fault occurs in the system.
• METERINGCONTROL
The system can enable metering in
METERINGCONTROL mode. This is the
actual status during normal operation. The
urea-water solution is injected in this mode.
In this mode, the pump is actuated in such
a way thata defined pressure is established.
This pressure is monitored. If the pressure
progression overshoots or undershoots
defined parameters, a fault is detected and
the system assumes
PRESSUREREDUCTION mode. These
faults are reset on return to
METERINGCONTROL mode.
PRESSUREREDUCTION mode is also
assumed if terminal 15 is switched off or
another fault occurs in the system.
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PRESSUREREDUCTION
Metering enable is cancelled on entering
PRESSUREREDUCTION mode.
This status reduces the pressure in the
delivery module, metering line and the
metering module after
PRESSURECONTROL mode. For this
purpose, the reversingvalve is opened andthe
pump actuated at a certain value, the metering
valve is closed.
PRESSUREREDUCTION mode ends when
the pressure drops below a certain value. The
system assumes NOPRESSURECONTROL
mode if the pressure threshold is reached
(undershot) within a defined time.
The system signals a fault if the pressure does
not drop below the threshold after a defined
time has elapsed. In this case or also in the
case of another fault, the system assumes
NOPRESSURECONTROL mode.
NOPRESSURECONTROL mode is also
assumed when terminal 15 is switched on.
AFTERRUN
The system is shut down in AFTERRUN
mode.
If terminal 15 is switched on again before
afterrun has been completed, afterrun is
cancelled and STANDBY mode is assumed. If
this is not the case the system goes through
the submodes of AFTERRUN.
• TEMPWAIT (catalytic converter
cooling phase)
In AFTERRUN mode, TEMPWAIT
submode is initially assumed if the system
is filled. This is intended to prevent
excessively hot exhaust gasses being
drawn into the SCR system.
The duration of the cooling phase is
determined by the exhaust gas
temperature. EMPTYING submode is
assumed after this time, in which the
exhaust system cools down, has elapsed.
EMPTYING submode is also assumed if a
fault occurs in the system.
If terminal 15 is switched on in this status,
STANDBY mode is assumed.
• EMPTYING
The system assumes
AFTERRUN_EMPTYING submode after
the cooling phase. The pressure line and
the delivery module are emptied in this
submode. Theurea-water solution is drawn
back into the active reservoir by opening
the reversing valve, actuating the pump and
opening the metering valve. This is
intended to prevent the urea-water solution
freezing inthe metering lineor the metering
module.
The level inthe metering line is calculated in
this mode.
PRESSURECOMPENSATION mode is
assumed if the metering line is empty.
PRESSURECOMPENSATION mode is
also assumed if a fault occurs in the system.
If terminal 15 is switched on, STANDBY
mode is assumed.
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• PRESSURECOMPENSATION (intake
line - ambient pressure)
After the system has been completely
emptied, PRESSURECOMPENSATION
submode is assumed. In this status the
pump is switched off, the reversing valve is
then closed followed by the metering valve
after a delay. The time interval between
switching off the pump and closing the
valve prevents a vacuum forming in the
intake line; pressure compensation
between the intake line and ambient
pressure takes place.
Warning and shut-down scenario
The SCR system is relevant to the vehicle
complying with the exhaust emission
regulations - it is a prerequisite for approval/
homologation! If the system fails, the approval
will be invalidated and the vehicle must no
longer be operated. A very plausible case
leading to the system failure is that the ureawater solution runs out.
After executing the steps correctly the
system assumes
WAITING_FOR_SHUTOFF submode.
WAITING_FOR_SHUTOFF is also
assumed if a fault occurs in the system.
If terminal 15 is switched on, STANDBY
mode is assumed.
• WAITING_FOR_SHUTOFF (shutting
down SCR)
The control unit is shut down and switched
off.
Vehicle operation is no longer permitted
without the urea-water solution, therefore, the
engine will no longer start.
To ensure the driver is not caught out, a
warning and shut-down scenario is provided
that begins at a sufficiently long time before
the vehicle actually shuts down so that the
driver can either conveniently top up the ureawater solution himself or have it topped up.
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Warning scenario
The warning scenario begins when the level
drops below the "Warning" level sensor in the
active reservoir. At this point, the active
reservoir is still approximately 50 % full with
urea-water solution. The level is then
determined as a defined volume (depending
on type of vehicle).
From this point on, the actual consumption of
the urea-water solution is subtracted from this
value. The mileage is recorded when the
amount of 2500 ml is reached.
A countdown from 1000 mls now takes place
- irrespective of the actual consumption of the
urea-water solution. The driver receives a
priority 2 (yellow) check control message
showing the remaining range.
53 - CC message in CID, range < 1000 mls
The driver receives a priority 1 (red) check
control message as from 200 mls.
52 - CC message in instrument
cluster, range < 1000 mls
If the vehicle is equipped with an on-board
computer (CID - Central Information Display),
instruction will also be displayed.
54 - CC message in instrument
cluster, range < 200 mls
In this case the following message is shown in
the CID:
55 - CC message in CID, range < 200 mls
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Shut-down scenario
If the range reaches 0 mls, similar as to in the
fuel gauge, three dashes are shown instead of
the range.
56 - CC message in instrument
cluster, range = 0 mls
The check control message in the CID
changes and shows that the engine can no
longer be started.
Exhaust fluid incorrect
If the systemis filled with anincorrect medium,
this will become apparent after several
hundred miles (kilometres) later by elevated
nitrogen oxide values in the exhaust gas
despite adequate injection of the supposed
urea-water solution. The system recognizes
an incorrect medium when certain limits are
exceeded. From this point on, a warning and
shut-down scenario is also initiated that allows
a remaining range of 200 mls.
58 - CC message in instrument
cluster in the case of
incorrect exhaust fluid
The exclamation mark in the symbol identifies
the fault in the system.
In this case, the message in the CID informs
the driver to go to the nearest workshop.
57 - CC message in CID, range = 0 mls
In this case, it will no longer be possible to start
the engine if it has been shut down for longer
than three minutes. This is intended to allow
the driver to move out of a hazardous situation
if necessary.
If the system is refilled only after engine start
has been disabled, the logic of the refill
recognition system is changed in this special
case, enabling faster refill.
59 - CC message in CID in the case of incorrect exhaust fluid
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9
Refilling
The active and passive reservoirs can be
refilled with urea-water solution either by the
service workshop or by the customer himself.
The system can be refilled without any
problems with thevehicle on an inclineof up to
5° in any direction. In this case, 90 % of the
maximum possible fill is still achieved.
The volume of the urea-water solution
reservoir is designed such that the range is
large enough to cover one oil change interval.
This means the "normal" refill takes place as
part of the servicing work in the workshop. If,
however, the supply of urea-water solution
should run low prematurely due to
extraordinary driving profile, itis possible to top
up a smaller quantity.
Refilling in service workshop
Refilling in the service workshop refers to the
routine refill as part of the oil change
procedure. This takes place at the latest after:
• 13000 mls on the E90,
• 11000 mls on the E70 or
• one year.
In this case, the system must be emptied first
in order to remove older urea-water solution.
This takes place via the extractor connections
in the transfer line. Although a small residual
quantity always remains in the reservoirs, it is
negligible.
Topping up
Any required quantity can be topped up if the
urea-water solution reserve does not last up to
the next oil change. Ideally, this quantity
should only be as much as is required to reach
the next oil change, as the system is then
emptied.
94
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