Actron CP7677 User Manual

Auto TroubleShooter

™

OPERATING

INSTRUCTIONS

Index

Safety Precautions ......................................... 2

Vehicle Service Information ........................... 3

Visual Inspection ............................................ 3

Electrical Specifications ............................... 34

Warranty ..................................................... 104

1. Multimeter Basic Functions

Functions and Display Definitions ............ 4

Setting the Range ..................................... 6

Battery and Fuse Replacement................ 7

Measuring DC Voltage.............................. 8

Measuring AC Voltage.............................. 8

Measuring Resistance .............................. 9

Measuring DC Current.............................. 9

Testing f or C on ti nu i ty .............................. 10

Testing Diodes ........................................ 11

Measuring Engine RPM.......................... 11

Measuring Dwell ..................................... 12

2. Automotive Testing with the CP7677

General Testing ...................................... 13

- Testing Fuses ...................................... 13

- Testing Switches ................................. 13

- Testing Solenoids and Relays ............ 14

Starting / Charging System Testing ....... 15

- No Load Battery Test .......................... 15

- Engine Off Battery Current Draw ........ 15

CP7677

- Cranking Voltage/Battery Load Test ... 16

- Voltage Drops ...................................... 17

- Charging System Voltage Test ........... 18

Ignition System Testing .......................... 19

- Igni t io n C o il Te s ti ng ............................. 19

- Ignition System Wires.......................... 21

- Hall Effect Sensors/Switches .............. 22

- Magnetic Pick-Up Coils ....................... 23

- Reluctance Sensors ............................ 23

- Igni t io n C o il Sw i tc hi n g A ct i on .............. 24

Fuel System Testing ............................... 25

- Testing GM C-3 Mixture Control

Solenoid Dwell .................................... 25

- Measuring Fuel Injector Resistance ... 26

Testing Engine Sensors .......................... 27

- Oxygen (O2) Type Sensors ................. 27

- Temperature Type Sensors ................ 29

- Position Type Sensors –
Throttle and EGR Valve Position,

Vane Air Flow ...................................... 30

- Manifold Absolute Pressure (MAP) and
Barometric Pressure (BARO) Sensors 31

- Mass Air Flow (MAF) Sensors ............ 32

Instrucciones en español ....35

Instructions en français.......6 9

1

SAFETY GUIDELINES

TO PREVENT ACCIDENTS THAT COULD RESULT IN SERIOUS INJURY

AND/OR DAMAGE TO YOUR VEHICLE OR TEST EQUIPMENT,

CAREFULLY FOLLOW THESE SAFETY RULES AND TEST PROCEDURES

• Always wear approved eye protection.

• Always operate the vehicle in a well ventilated area. Do not inhale exhaust gases
– they are very poisonous!

• Always keep yourself, tools and test equipment away from all moving or hot
engine parts.

• Always make sure the vehicle is in park (Automatic transmission) or neutral
(manual transmission) and that the parking brake is firmly set. Block the drive
wheels.

• Never lay tools on vehicle battery. You may short the terminals together causing
harm to yourself, the tools or the battery.

• Never smoke or have open flames near vehicle. Vapors from gasoline and
charging battery are highly flammable and explosive.

• Never leave vehicle unattended while running tests.

• Always keep a fire extinguisher suitable for gasoline/electrical/chemical fires
handy.

• Always use extreme caution when working around the ignition coil, distributor
cap, ignition wires, and spark plugs. These components contain High Voltage
when the engine is running.

• Always turn ignition key OFF when connecting or disconnecting electrical
components, unless otherwise instructed.

• Always follow vehicle manufacturer’s warnings, cautions and service procedures.

CAUTION:

Some vehicles are equipped with safety air bags. You

manual cautions when working around the air bag components or wiring. If the
cautions are not followed, the air bag may open up unexpectedly, resulting in personal
injury. Note that the air bag can still open up several minutes after the ignition key is
off (or even if the vehicle battery is disconnected) because of a special energy reserve
module.

All information, illustrations and specifications contained in this manual are based on the latest
information available from industry sources at the time of publication. No warranty (expressed
or implied) can be made for its accuracy or completeness, nor is any responsibility assumed by
Actron Manufacturing Co. or anyone connected with it for loss or damages suffered through
reliance on any information contained in this manual or misuse of accompanying product. Actron
Manufacturing Co. reserves the right to make changes at any time to this manual or accompa­nying product without obligation to notify any person or organization of such changes.

2

must

follow vehicle service

Vehicle Service Manual – Sources For Service
Information

The following is a list of sources to obtain vehicle service information for your specific
vehicle.

• Contact your local Automotive Dealership Parts Department.

• Contact local retail auto parts stores for aftermarket vehicle service information.

• Contact your local library. Libraries often allow you to check-out automotive service

manuals.

Do a Thorough Visual Inspection

Do a thorough visual and “hands-on” underhood inspection before starting any
diagnostic procedure! You can find the cause of many problems by just looking,
thereby saving yourself a lot of time.

• Has the vehicle been serviced
recently? Sometimes things get
reconnected in the wrong place, or
not at all.

• Don’t take shortcuts. Inspect hoses
and wiring which may be difficult to
see due to location.

• Inspect the air cleaner and
ductwork for defects.

• Check sensors and actuators for
damage.

• Inspect ignition wires for:

- Damaged terminals.

- Split or cracked spark plug boots

- Splits, cuts or breaks in the ignition
wires and insulation.

• Inspect all vacuum hoses for:

- Correct routing. Refer to vehicle
service manual, or Vehicle Emis­sion Control Information(VECI)
decal located in the engine com­partment.

- Pinches and kinks.

- Splits, cuts or breaks.

• Inspect wiring for:

- Contact with sharp edges.

- Contact with hot surfaces, such as
exhaust manifolds.

- Pinched, burned or chafed insula­tion.

- Proper routing and connections.

• Check electrical connectors for:

- Corrosion on pins.

- Bent or damaged pins.

- Contacts not properly seated in
housing.

- Bad wire crimps to terminals.

3

Section 1. Multimeter Basic Functions

Digital multimeters or DMMs have many special features and functions. This section
defines these features and functions, and explains how to use these functions to make
various measurements.

12

10

11

9

8

7

6

Alligator Clip Adapters

Some multimeter tests and measurements are more easily done using
alligator clips instead of test prods. For these tests, push the crimp end of the
alligator clip onto the test prod. If the crimp on the alligator clip becomes loose,
then remove the alligator clip from the test prod and re-crimp using a pair of
pliers.

5

4

3

2

1

4

Functions and Display Definitions

1. ROTARY SWITCH

Switch is rotated to select a function.

2. DC VOLTS

This function is used for measuring DC
(Direct Current) Voltages in the range
of 0 to 1000V.

3. OHMS

This function is used for measuring the
resistance of a component in an elec­trical circuit in the range of 0.1Ω to
20MΩ. (Ω is the electrical symbol for
Ohms)

4.

DIODE CHECK / CONTINUITY TESTS

This function is used to check whether a
diode is good or bad. It is also used for
fast continuity checks of wires and ter­minals. An audible tone will sound if a
wire and terminal are good.

5. HOLD

Press HOLD button to retain data on
display. In the hold mode, the "H" an­nunciator is displayed.

6. TEST LEAD JACKS

BLACK Test Lead is al-

ways inserted in the COM
jack.

RED Test Lead is in­serted in the jack corre­sponding to the multim­eter rotary switch setting.

DC VOLTS

DC AMPS

RPM

DWELL

OHMS

AC VOLTS

DIODES

CONTINUITY

Always connect TEST LEADS to the mul­timeter before connecting them to the
circuit under test!!

7. AC VOLTS

This function is used for measuring AC
Voltages in the range of 0 to 750V.

8. DC AMPS

This function is used for measuring DC
(Direct Current) Amps in the range of 0
to 10A.

9. DWELL

This function is used for measuring
DWELL on distributor ignition systems,
and solenoids.

10. TACH

This function is used for measuring
engine speed (RPM).

11. ON/OFF

Press to turn power ON. Press again to
turn power OFF.

12. DISPLAY

Used to display all measurements and
multimeter information.

Low Battery – If this symbol appears
in the lower left corner of the display,

then replace the inter­nal 9V battery. (See
Fuse and Battery re­placement on page 7.)

Overrange Indication

– If “1” or “-1” appears
on the left side of the
display, then the multi­meter is set to a range
that is too small for the
present measurement
being taken. Increase
the range until this dis-

appears. If it does not
disappear after all the ranges for a
particular function have been tried, then
the value being measured is too large
for the multimeter to measure. (See
Setting the Range on page 6.)

Zero Adjustment

The multimeter will automatically zero on
the Volts, Amps and RPM functions.

Automatic Polarity Sensing

The multimeter display will show a minus (-)
sign on the DC Volts and DC Amps functions
when test lead hook-up is reversed.

5

Setting the Range

Two of the most commonly asked ques­tions about digital multimeters are What
does Range mean? and How do I know
what Range the multimeter should be
set to?

What Does Range mean?

Range refers to the largest value the
multimeter can measure with the rotary
switch in that position. If the multimeter
is set to the 20V DC range, then the
highest voltage the multimeter can mea­sure is 20V in that range.

EXAMPLE: Measuring Vehicle Battery
Voltage (See Fig. 1)

Fig. 1

Black

Red

Now assume we set the multimeter to
the 2V range. (See Fig. 2)

The multimeter display now shows a “1”
and nothing else. This means the multi­meter is being overranged or in other
words the value being measured is larger
than the current range. The range should
be increased until a value is shown on
the display. If you are in the highest
range and the multimeter is still showing
that it is overranging, then the value
being measured is too large for the mul­timeter to measure.

How do I know what Range the multi­meter should be set to?

The multimeter should be set in the
lowest possible range without
overranging.

EXAMPLE: Measuring an unknown re­sistance

Let’s assume the multimeter is con­nected to an engine coolant sensor with
unknown resistance. (See Fig. 3)

Fig. 3

Let’s assume the multimeter is con­nected to the battery and set to the 20V
range.

The display reads 12.56. This means
there is 12.56V across the battery termi­nals.

Fig. 2

Black

Red

Red

Black

Start by setting the multimeter to the
largest OHM range. The display reads

0.0Ω or a short circuit.
This sensor can’t be shorted so reduce

the range setting until you get a value of
resistance.

At the 200KΩ range the multimeter mea­sured a value of 4.0. This means there is
4KΩ of resistance across the engine
coolant sensor terminals. (See Fig. 4)

If we change the multimeter to the 20KΩ
range (See Fig. 5) the display shows a

6

Fig. 4

value of

3.87KΩ. The
actual value of
resistance is

3.87KΩ and not
4KΩ that was
measured in
the 200KΩ
range. This is
very important
because if the
manufacturer
specifications
say that the
sensor should
read 3.8-3.9KΩ
at 70°F then on
the 200KΩ
range the sensor would be defective, but
at the 20KΩ range it would test good.

Now set the multimeter to the 2KΩ range.
(See Fig. 6) The
display will indi­cate an
overrange con­dition because

3.87KΩ is larger
than 2KΩ.

This example
shows that by
decreasing the
range you in­crease the ac­curacy of your
measurement.
When you
change the
range, you
change the lo­cation of the decimal point. This changes

Fig. 5

Fig. 6

the accuracy of the measurement by ei­ther increasing or decreasing the number
of digits after the decimal point.

Battery and Fuse
Replacement

Important: A 9 Volt battery must be in­stalled before using the digital multim­eter. (see procedure below for installa­tion)

Battery Replacement

1. Turn multimeter OFF.

2. Remove test leads from
multimeter.

3. Remove screw from battery
cover.

4. Remove battery cover.

5. Install a new 9 Volt battery.

6. Re-assemble multimeter.

Fuse Replacement

1. Turn multimeter OFF.

2. Remove test leads from
multimeter.

3. Remove rubber holster.

4. Remove screw from battery
cover, battery cover, and battery.

5. Remove screws from back of
multimeter.

6. Remove back cover.

7. Remove fuse.

8. Replace fuse with same size and
type as originally installed.

Use a 1/4" x 1-1/4", 10A, 250V, fast
acting fuse or a 5mm x 20mm
315mA, 250V fast acting fuse.

9. Re-assemble multimeter.

7

Measuring DC Voltage

This multimeter can be used to measure
DC voltages in the range from 0 to 1000V.
You can use this multimeter to do any DC
voltage measurement called out in the
vehicle service manual. The most com­mon applications are measuring voltage
drops, and checking if the correct voltage
arrived at a sensor or a particular circuit.

To measure DC Voltages (see Fig. 7):

Fig. 7

Red

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Connect RED test lead to positive
(+) side of voltage source.

4. Connect BLACK test lead to nega­tive (-) side of voltage source.

NOTE: If you don’t know which side

is positive (+) and which side is nega­tive (-), then arbitrarily connect the
RED test lead to one side and the
BLACK to the other. The multimeter
automatically senses polarity and will
display a minus (-) sign when nega­tive polarity is measured. If you
switch the RED and BLACK test
leads, positive polarity will now be
indicated on the display. Measuring
negative voltages causes no harm
to the multimeter.

5. Turn multimeter rotary switch to
desired voltage range.

If the approximate voltage is unknown,
start at the largest voltage range and
decrease to the appropriate range as
required. (See Setting the Range on
page 6)

Black

test lead jack.

6. View reading on display - Note
range setting for correct units.

NOTE: 200mV = 0.2V

Measuring AC Voltage

This multimeter can be used to measure
AC voltages in the range from 0 to 750V.

To measure AC Voltages (see Fig. 8):

Fig. 8

Red

Black

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

test lead jack.

3. Connect RED test lead to one side
of voltage source.

4. Connect BLACK test lead to other
side of voltage source.

5. Turn multimeter rotary switch to
desired voltage range.

If the approximate voltage is un­known, start at the largest voltage
range and decrease to the appropri­ate range as required. (See Setting
the Range on page 6)

6. View reading on display - Note
range setting for correct units.

NOTE: 200mV = 0.2V

8

Measuring Resistance

Resistance is measured in electrical
units called ohms (Ω). The digital multi­meter can measure resistance from 0.1Ω
to 20MΩ or (20,000,000 ohms). Infinite
resistance is shown with a “1” on the left
side of display (See Setting the Range
on page 6). You can use this multimeter
to do any resistance measurement called
out in the vehicle service manual. Test­ing ignition coils, spark plug wires, and
some engine sensors are common uses
for the OHMS (Ω) function.

To measure Resistance (see Fig. 9):

Fig. 9

Unknown

Resistance

Red Black

1. Turn circuit power OFF.

To get an accurate resistance mea­surement and avoid possible damage
to the digital multimeter and electrical
circuit under test, turn off all electrical
power in the circuit where the resis­tance measurement is being taken.

2. Insert BLACK test lead into COM
test lead jack.

3. Insert RED test lead into

4. Turn multimeter rotary switch to
200

Ω range.

Touch RED and BLACK multimeter
leads together and view reading on
display.

Display should read typically 0.2Ω to

1.5Ω.
If display reading was greater than

1.5Ω, check both ends of test leads
for bad connections. If bad connec­tions are found, replace test leads.

5. Connect RED and BLACK test
leads across component where
you want to measure resistance.

When making resistance measure-

test lead jack.

ments, polarity is not important. The
test leads just have to be connected
across the component.

6. Turn multimeter rotary switch to
desired OHM range.

If the approximate resistance is un­known, start at the largest OHM
range and decrease to the appropri­ate range as required. (See Setting
the Range on page 6)

7. View reading on display - Note
range setting for correct units.

NOTE: 2KΩ = 2,000Ω; 2MΩ =
2,000,000Ω

If you want to make precise resis­tance measurements, then subtract
the test lead resistance found in Step
4 above from the display reading in
Step 7. It is a good idea to do this for
resistance measurements less than
10Ω.

Measuring DC Current

This multimeter can be used to measure
DC current in the range from 0 to 10A. If
the current you are measuring exceeds
10A, the internal fuse will blow (see Fuse
Replacement on page 7). Unlike voltage
and resistance measurements where the
multimeter is connected across the com­ponent you are testing, current measure­ments must be made with the multimeter
in series with the component. Isolating
current drains and short circuits are some
DC Current applications.

To measure DC Current (see Figs. 10 &

11):

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into "10A"
test lead jack or "mA" test lead
jack.

3. Disconnect or electrically open cir­cuit where you want to measure
current.

This is done by:

• Disconnecting wiring harness.

• Disconnecting wire from screw-on

type terminal.

• Unsolder lead from component if

9

Fig. 10

DC
Voltage
Source

Black

Fig. 11

DC
Voltage

Source

Electrical

Device

Red

Electrical

Device

Red

Testing for Continuity

Continuity is a quick way to do a resis­tance test to determine if a circuit is
open or closed. The multimeter will beep
when the circuit is closed or shorted, so
you don’t have to look at the display.
Continuity checks are usually done when
checking for blown fuses, switch opera­tion, and open or shorted wires.

To measure Continuity (see Fig. 12):

Fig. 12

Black

working on printed circuit boards.

• Cut wire if there is no other pos­sible way to open electrical circuit.

4. Connect RED test lead to one side
of disconnected circuit.

5. Connect BLACK test lead to re­maining side of disconnected cir­cuit.

6. Turn multimeter rotary switch to
10A DC position, or 200mA posi­tion.

7. View reading on display.

If minus (-) sign appears on display,
then reverse RED and BLACK test
leads.

Red

Black

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

test lead jack.

3. Turn multimeter rotary switch to

function.

4. Touch RED and BLACK test leads
together to test continuity.

Listen for tone to verify proper op­eration.

5. Connect RED and BLACK test
leads across component where
you want to check for continuity.

Listen for tone:

• If you hear tone – Circuit is closed

or shorted.

• If you don’t hear tone – Circuit is

open.

10

Testing Diodes

A diode is an electrical component that
allows current to only flow in one direc­tion. When a positive voltage, generally
greater than 0.7V, is applied to the an­ode of a diode, the diode will turn on and
allow current to flow. If this same volt­age is applied to the cathode, the diode
would remain off and no current would
flow. Therefore, in order to test a diode,
you must check it in both directions (i.e.
anode-to-cathode, and cathode-to-an­ode). Diodes are typically found in alter­nators on automobiles.

Performing Diode Test (see Fig. 13):

Fig. 13

Cathode

Anode

Red

Black

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Turn multimeter rotary switch to

4. Touch RED and BLACK test leads
together to test continuity.

Check display – should reset to 0.00.

5. Disconnect one end of diode from
circuit.

Diode must be totally isolated from
circuit in order to test its functional­ity.

6. Connect RED and BLACK test
leads across diode and view dis­play.

Display will show one of three things:

• A typical voltage drop of around

0.7V.

• A voltage drop of 0 volts.

• A “1” will appear indicating the mul-

timeter is overranged.

test lead jack.

function.

7. Switch RED and BLACK test leads
and repeat Step 6.

8. Test Results

If the display showed:

• A voltage drop of 0 volts in both

directions, then the diode is shorted
and needs to be replaced.

• A “1” appears in both directions,

then the diode is an open circuit
and needs to be replaced.

• The diode is good if the display

reads around 0.5V–0.7V in one di­rection and a “1” appears in the
other direction indicating the multi­meter is overranged.

Measuring Engine RPM

RPM refers to revolutions per minute.
When using this function you must multi­ply the display reading by 10 to get actual
RPM. If display reads 200 and the multim­eter is set to 6 cylinder RPM, the actual
engine RPM is 10 times 200 or 2000 RPM.

To measure Engine RPM (see Fig. 14):

Fig. 14

Typical

Ignition

Coil

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Connect RED test lead to TACH
(RPM) signal wire.

• If vehicle is DIS (Distributorless

• For all vehicles with distributors,

11

Red

Black

Ground

test lead jack.

Ignition System), then connect RED
test lead to the TACH signal wire
going from the DIS module to the
vehicle engine computer. (refer to
vehicle service manual for location
of this wire)

connect RED test lead to negative
side of primary ignition coil. (refer
to vehicle service manual for loca­tion of ignition coil)

4. Connect BLACK test lead to a good
vehicle ground.

5. Turn multimeter rotary switch to
correct CYLINDER selection.

6. Measure engine RPM while engine
is cranking or running.

7. View reading on display.

• Remember to multiply display read-

ing by 10 to get actual RPM.

If display reads 200, then actual en­gine RPM is 10 times 200 or 2000
RPM.

Measuring Dwell

Dwell measuring was extremely impor­tant on breaker point ignition systems of
the past. It referred to the length of time,
in degrees, that the breaker points re­mained closed, while the camshaft was
rotating. Today’s vehicles use electronic
ignition and dwell is no longer adjust­able. Another application for dwell is in
testing the mixture control solenoid on
GM feedback carburetors.

To measure Dwell (see Fig. 15):

Fig. 15

Typical

Ignition

Coil

Red

Black

Ground

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Connect RED test lead to DWELL
signal wire.

test lead jack.

• If measuring DWELL on breaker
point ignition systems, connect
RED test lead to negative side of
primary ignition coil. (refer to ve­hicle service manual for location of
ignition coil)

• If measuring DWELL on GM mix­ture control solenoids, connect
RED test lead to ground side or
computer driven side of solenoid.
(refer to vehicle service manual for
solenoid location)

• If measuring DWELL on any arbi­trary ON/OFF device, connect RED
test lead to side of device that is
being switched ON/OFF.

4. Connect BLACK test lead to a good
vehicle ground.

5. Turn multimeter rotary switch to
correct DWELL CYLINDER posi­tion.

6. View reading on display.

12

Section 2. Automotive Testing

The digital multimeter is a very useful
tool for trouble-shooting automotive elec­trical systems. This section describes
how to use the digital multimeter to test
the starting and charging system, igni­tion system, fuel system, and engine
sensors. The digital multimeter can also
be used for general testing of fuses,
switches, solenoids, and relays.

General Testing

The digital multimeter can be used to
test fuses, switches, solenoids, and re­lays.

Testing Fuses

This test checks to see if a fuse is blown.
You can use this test to check the internal
fuses inside the digital multimeter.

To test Fuses (see Fig. 16):

Fig. 16

Fuse

Red

Black

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Turn multimeter rotary switch to

4. Touch RED and BLACK test leads
together to test continuity.

Listen for tone to verify proper op­eration.

5. Connect RED and BLACK test
leads to opposite ends of fuse.

Listen for tone:

test lead jack.

function.

• If you hear tone - Fuse is good.

• If you don’t hear tone - Fuse is

blown and needs to be replaced.

NOTE: Always replace blown fuses
with same type and rating.

Testing Switches

This test checks to see if a switch
“Opens” and “Closes” properly.

To test Switches (see Fig. 17):

Fig. 17

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Turn multimeter rotary switch to

function.

4. Touch RED and BLACK test leads
together to test continuity.

Listen for tone to verify proper op­eration.

5. Connect BLACK test lead to one
side of switch.

6. Connect RED test lead to other
side of switch.

Listen for tone:

• If you hear tone - The switch is

closed.

• If you don’t hear tone - The switch

is open.

7. Operate switch.

Listen for tone:

Typical "Push"

Button Switch

Red

Black

test lead jack.

13

• If you hear tone - The switch is
closed.

• If you don’t hear tone - The switch
is open.

8. Repeat Step 7 to verify switch op­eration.

Good Switch:

OFF as you operate switch.

Bad Switch:

always OFF as you operate switch.

Tone turns ON and

Tone always ON or tone

Testing Solenoids and Relays

This test checks to see if a solenoid or
relay have a broken coil. If the coil tests
good, it is still possible that the relay or
solenoid are defective. The relay can
have contacts that are welded or worn
down, and the solenoid may stick when
the coil is energized. This test does not
check for those potential problems.

To test Solenoids and Relays (see Fig.

18):

Fig. 18

Relay or

Solenoid

Red

Black

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Turn multimeter rotary switch to
200

Ω function.

Most solenoids and relay coil resis­tances are less than 200Ω. If meter
overranges, turn multimeter rotary
switch to next higher range. (see
Setting the Range on page 6)

test lead jack.

4. Connect BLACK test lead to one
side of coil.

5. Connect RED test lead to other
side of coil.

6. View reading on display.

• Typical solenoid / relay coil resis-

tances are 200Ω or less.

• Refer to vehicle service manual for

your vehicles resistance range.

7. Test Results

Good Solenoid / Relay Coil:

in Step 6 is within manufacturers
specification.

Display

Bad Solenoid / Relay Coil:

• Display in Step 6 is not within manu-

facturers specifications.

• Display reads overrange on every

ohms range indicating an open cir­cuit.

NOTE: Some relays and solenoids
have a diode placed across the coil.
To test this diode see Testing Di­odes on page 11.

14

Starting/Charging System Testing

The starting system “turns over” the engine. It consists of the battery, starter motor,
starter solenoid and/or relay, and associated wiring and connections. The charging
system keeps the battery charged when the engine is running. This system consists
of the alternator, voltage regulator, battery, and associated wiring and connections.
The digital multimeter is a useful tool for checking the operation of these systems.

No Load Battery Test

Before you do any starting/charging sys­tem checks, you must first test the bat­tery to make sure it is fully charged.

Test Procedure (see Fig. 19):

Fig. 19

Red

Black

1. Turn Ignition Key OFF.

2. Turn ON headlights for 10 sec­onds to dissipate battery surface
charge.

3. Insert BLACK test lead into COM
test lead jack.

4. Insert RED test lead into

5. Disconnect positive (+) battery
cable.

6. Connect RED test lead to positive
(+) terminal of battery.

7.

Connect BLACK test lead to nega­tive (-) terminal of battery.

8. Turn multimeter rotary switch to
20V DC range.

9. View reading on display.

10.Test Results.

Compare display reading in Step 9
with the following chart.

test lead jack.

Voltage Battery is Charged

12.60V
or greater 100%

12.45V 75%

12.30V 50%

12.15V 25%

If battery is not 100% charged, then
charge it before doing anymore starting/
charging system tests.

Percent

Engine Off Battery
Current Draw

This test measures the amount of cur­rent being drawn from the battery when
the ignition key and engine are both off.
This test helps to identify possible
sources of excessive battery current
drain, which could eventually lead to a
“dead” battery.

1. Turn Ignition Key and all accesso­ries OFF.

Make sure trunk, hood, and dome
lights are all OFF.

(See Fig. 20)

2. Insert BLACK test lead into COM
test lead jack.

3. Insert RED test lead into "A" (or
"mA") test lead jack.

Fig. 20

Black

Red

15

4. Disconnect positive (+) battery
cable.

5. Connect RED test lead to positive
(+) battery terminal.

6. Connect BLACK test lead to posi­tive (+) battery cable.

NOTE: Do not start vehicle during this
test, because multimeter damage may
result.

7. Turn multimeter rotary switch to
10A DC (or 200 mA) position.

8. View reading on display.

• Typical current draw is 100mA.

(1mA = 0.001A)

• Refer to vehicle service manual for

manufacturers specific Engine Off
Battery Current Draw.

NOTE: Radio station presets and
clocks are accounted for in the 100mA
typical current draw.

9. Test Results.

Normal Current Draw:

ing in Step 8 is within manufacturers
specifications.

Display read-

Excessive Current Draw:

- Display reading in Step 8 is well out-

side manufacturers specifications.

- Remove Fuses from fuse box one

at a time until source of excessive
current draw is located.

- Non-Fused circuits such as head-

lights, relays, and solenoids should
also be checked as possible cur­rent drains on battery.

- When source of excessive current

drain is found, service as necessary.

Cranking Voltage ­Battery Load Test

This test checks the battery to see if it is
delivering enough voltage to the starter
motor under cranking conditions.

Test Procedure (see Fig. 21):

1. Disable ignition system so vehicle
won’t start.

Disconnect the primary of the igni­tion coil or the distributor pick-up coil

Fig. 21

Red Black

or the cam/crank sensor to disable
the ignition system. Refer to vehicle
service manual for disabling proce­dure.

2. Insert BLACK test lead into COM
test lead jack.

3. Insert RED test lead into

4. Connect RED test lead to positive
(+) terminal of battery.

5.

Connect BLACK test lead to nega­tive (-) terminal of battery.

6. Turn multimeter rotary switch to
20V DC range.

7. Crank engine for 15 seconds con­tinuously while observing display.

8. Test Results.

Compare display reading in Step 7
with chart below.

Voltage Temperature

9.6V or greater70 °F and Above

9.5V 60 °F

9.4V 50 °F

9.3V 40 °F

9.1V 30 °F

8.9V 20 °F

8.7V 10 °F

8.5V 0 °F

If voltage on display corresponds to
above voltage vs. temperature chart,
then cranking system is normal.

If voltage on display does not corre­spond to chart, then it is possible that
the battery, battery cables, starting sys­tem cables, starter solenoid, or starter
motor are defective.

16

test lead jack.

Voltage Drops

This test measures the voltage drop across
wires, switches, cables, solenoids, and
connections. With this test you can find
excessive resistance in the starter sys­tem. This resistance restricts the amount
of current that reaches the starter motor
resulting in low battery load voltage and a
slow cranking engine at starting.

Test Procedure (see Fig. 22):

1. Disable ignition system so vehicle
won’t start.

Disconnect the primary of the igni­tion coil or the distributor pick-up coil
or the cam/crank sensor to disable
the ignition system. Refer to vehicle
service manual for disabling proce­dure.

2. Insert BLACK test lead into COM
test lead jack.

3. Insert RED test lead into

4. Connect test leads.

Refer to Typical Cranking Voltage
Loss Circuit (Fig. 22).

•

Connect RED and BLACK test leads
alternately between 1 & 2, 2 & 3, 4 &
5, 5 & 6, 6 & 7, 7 & 9, 8 & 9, and 8 &

10.

5. Turn multimeter rotary switch to
200mV DC range.

test lead jack.

If multimeter overranges, turn multim­eter rotary switch to the 2V DC range.
(See Setting the Range on page 6)

6. Crank engine until steady reading
is on display.

• Record results at each point as

displayed on multimeter.

• Repeat Step 4 & 5 until all points

are checked.

7. Test Results –

Estimated Voltage Drop of Starter
Circuit Components

Component Voltage

Switches 300mV
Wire or Cable 200mV
Ground 100mV
Battery Cable

Connectors 50mV
Connections 0.0V

• Compare voltage readings in Step

6 with above chart.

• If any voltages read high, inspect com-

ponent and connection for defects.

• If defects are found, service as

necessary.

Fig. 22 Typical Cranking Voltage

Loss Circuit

This is a representative sample of
one type of cranking circuit. Your
vehicle may use a different circuit
with different components or
locations. Consult your vehicle
service manual.

Starter

10

1

9

8

7

17

Solenoid

6

5

4

Red Black

3

2

6 8

7
9

5

4

3

2

Charging System Voltage Test

This test checks the charging system to
see if it charges the battery and pro­vides power to the rest of the vehicles
electrical systems (lights, fan, radio etc).

Test Procedure (see Fig. 23):

Fig. 23

Red Black

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Connect RED test lead to positive
(+) terminal of battery.

4.

Connect BLACK test lead to nega­tive (-) terminal of battery.

5. Turn multimeter rotary switch to
20V DC range.

6. Start engine - Let idle.

7. Turn off all accessories and view
reading on display.

• Charging system is normal if dis-

play reads 13.2 to 15.2 volts.

• If display voltage is not between

13.2 to 15.2 volts, then proceed to
Step 13.

test lead jack.

8. Open throttle and Hold engine
speed (RPM) between 1800 and
2800 RPM.

Hold this speed through Step 11 ­Have an assistance help hold speed.

9. View reading on display.

Voltage reading should not change
from Step 7 by more than 0.5V.

10.Load the electrical system by turn­ing on the lights, windshield wip­ers, and setting the blower fan on
high.

11.View reading on display.

Voltage should not drop down below
about 13.0V.

12.Shut off all accessories, return
engine to curb idle and shut off.

13.Test Results.

• If voltage readings in Steps 7, 9,

and 11 were as expected, then
charging system is normal.

• If any voltage readings in Steps 7,

9, and 11 were different then shown
here or in vehicle service manual,
then check for a loose alternator
belt, defective regulator or alterna­tor, poor connections, or open al­ternator field current.

• Refer to vehicle service manual for

further diagnosis.

18

Ignition System T esting

The ignition system is responsible for providing the spark that ignites the fuel in the cylinder.
Ignition system components that the digital multimeter can test are the primary and
secondary ignition coil resistance, spark plug wire resistance, hall effect switches/sensors,
reluctance pick-up coil sensors, and the switching action of the primary ignition coil.

Ignition Coil Testing

This test measures the resistance of the
primary and secondary of an ignition
coil. This test can be used for
distributorless ignition systems (DIS)
provided the primary and secondary ig­nition coil terminals are easily acces­sible.

Test Procedure:

1. If engine is HOT let it COOL down
before proceeding.

2. Disconnect ignition coil from ig­nition system.

3. Insert BLACK test lead into COM
test lead jack (see Fig. 24).

Fig. 24

Secondary

Coil

Typical Cylindrical

Ignition Coil

4. Insert RED test
lead into

test

Fig. 25

lead jack.

5. Turn multimeter
rotary switch to
200

Ω range.

6. Touch RED and
BLACK multim­eter leads to­gether and view
reading on dis­play.

7. Connect test leads.

• Connect RED test lead to primary
ignition coil positive (+) terminal.

• Connect BLACK test lead to primary
ignition coil negative (-) terminal.

• Refer to vehicle service manual for
location of primary ignition coil ter­minals.

8. View reading on display.

Subtract test lead resistance found
in Step 6 from above reading.

9. If vehicle is DIS, repeat Steps 7
and 8 for remaining ignition coils.

10.Test Results - Pri­mary Coil

• Typical resistance

BlackRed

range of primary
ignition coils is 0.3

- 2.0Ω.

• Refer to vehicle

service manual

Primary

Coil

for your vehicles
resistance range.

11.Turn multimeter
rotary switch to
200K

Ω range (see

Fig. 25).

Secondary

Coil

Red

Typical Cylindrical

Ignition Coil

Black

Primary

Coil

19

12.Move RED test lead to secondary
ignition coil terminal.

• Refer to vehicle service manual for

location of secondary ignition coil
terminal.

• Verify BLACK test lead is con-

nected to primary ignition coil nega­tive (-) terminal.

13.View reading on display.

14. If vehicle is DIS, repeat Steps 12
and 13 for remaining ignition coils.

15.Test Results - Secondary Coil

• Typical resistance range of sec-

ondary ignition coils is 6.0 - 30.0KΩ.

• Refer to vehicle service manual for

your vehicles resistance range.

16. Repeat test procedure for a HOT
ignition coil.

NOTE: It is a good idea to test
ignition coils when they are both hot
and cold, because the resistance of
the coil could change with tempera­ture. This will also help in diagnosing
intermittent ignition system prob­lems.

17.Test Results - Overall

Good Ignition Coil:

ings in Steps 10, 15 and 16 were
within manufacturers specification.

Bad Ignition Coil:

ings in Steps 10, 15 and 16 are not
within manufacturers specification.

Resistance read-

Resistance read-

20

Ignition System Wires

This test measures the resistance
of spark plug and coil tower wires
while they are being flexed. This
test can be used for distributorless
ignition systems (DIS) provided the
system does not mount the ignition
coil directly on the spark plug.

Test Procedure:

1. Remove ignition system wires
one at a time from engine.

• Always grasp ignition system

wires

on the boot when re-

moving.

• Twist the boots about a half turn

while pulling gently to remove them.

• Refer to vehicle service manual for

ignition wire removal procedure.

• Inspect ignition wires for cracks,

chaffed insulation, and corroded
ends.

NOTE: Some Chrysler products use
a “positive-locking” terminal electrode
spark plug wire. These wires can
only be removed from inside the dis­tributor cap. Damage may result if
other means of removal are at­tempted. Refer to vehicle service
manual for procedure.

NOTE: Some spark plug wires have
sheet metal jackets with the follow­ing symbol:
wire contains an “air gap” resistor
and can only be checked with an
oscilloscope.

2. Insert BLACK test lead into COM
test lead jack (see Fig. 26).

3. Insert RED test lead into

. This type of plug

test lead jack.

Fig. 26

Spark Plug Wire

4. Connect RED test lead to one end
of ignition wire and BLACK test
lead to other end.

5. Turn multimeter rotary switch to
200KΩ range.

6. View reading on display while flex­ing ignition wire and boot in sev­eral places.

• Typical resistance range is 3KΩ to

50KΩ or approximately 10KΩ per
foot of wire.

• Refer to vehicle service manual

for your vehicles resistance range.

• As you flex ignition wire, the dis-

play should remain steady.

7. Test Results

Good Ignition Wire:

is within manufacturers specifica­tion and remains steady while wire
is flexed.

Bad Ignition Wire:

erratically changes as ignition wire
is flexed or display reading is not
within manufacturers specification.

Display reading

Display reading

Black

Red

21

Hall Effect Sensors/Switches

Hall Effect sensors are used whenever
the vehicle computer needs to know
speed and position of a rotating object.
Hall Effect sensors are commonly used
in ignition systems to determine cam­shaft and crankshaft position so the ve­hicle computer knows the optimum time
to fire the ignition coil(s) and turn on the
fuel injectors. This test checks for proper
operation of the Hall Effect sensor /
switch.

Test Procedure (see Fig. 27):

1. Remove Hall Effect Sensor from
vehicle.

Refer to vehicle service manual for
procedure.

2. Connect 9V battery to sensor
POWER and GROUND pins.

• Connect positive(+) terminal of 9V

battery to sensor POWER pin.

• Connect negative(-) terminal of 9V

battery to sensor GROUND pin.

• Refer to illustrations for POWER

and GROUND pin locations.

• For sensors not illustrated refer to

vehicle service manual for pin lo­cations.

3. Insert BLACK test lead into COM
test lead jack.

4. Insert RED test lead into
test lead jack.

5. Connect RED test lead to sensor

SIGNAL pin.

6. Connect BLACK test lead to 9V

battery negative(-) pin.

7. Turn multimeter rotary switch to

function.

Multimeter should sound a tone.

8. Slide a flat blade of iron or mag-

netic steel between sensor and
magnet. (Use a scrap of sheet metal,

knife blade, steel ruler, etc.)

• Multimeter tone should stop and
display should overrange.

• Remove steel blade and multim­eter should again sound a tone.

• It is O.K. if display changes errati­cally after metal blade is removed.

• Repeat several times to verify re­sults.

9. Test Results

Good Sensor:

Multimeter toggles
from tone to overrange as steel blade
is inserted and removed.

Bad Sensor:

No change in multim­eter as steel blade is inserted and
removed.

Fig. 27

Black POWER

9V

POWER

GROUND

SIGNAL

Red

22

Iron or Steel

Sensor

Typical Hall

Effect Sensor

Jumper

Wires

Blade

Magnet

Chrysler Distributor

Hall Effect

GROUND SIGNAL

Ford Distributor

Hall Effect

POWER

GROUND

SIGNAL

Magnetic Pick-Up Coils – Reluctance Sensors

Reluctance sensors are used whenever
the vehicle computer needs to know
speed and position of a rotating object.
Reluctance sensors are commonly used
in ignition systems to determine cam­shaft and crankshaft position so the ve­hicle computer knows the optimum time
to fire the ignition coil(s) and turn on the
fuel injectors. This test checks the reluc­tance sensor for an open or shorted coil.
This test does not check the air gap or
voltage output of the sensor.

Test Procedure (see Fig. 28):

Fig. 28

Red

Reluctance

Sensor

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

test lead jack.

3. Connect RED test lead to either
sensor pin.

4. Connect BLACK test lead to re­maining sensor pin.

5. Turn multimeter rotary switch to
2K

Ω range.

6. View reading on display while flex­ing sensor wires in several places.

• Typical resistance range is 150 -

1000Ω.

• Refer to vehicle service manual for

your vehicles resistance range.

• As you flex sensor
wires, the display
should remain steady.

Ring

7. Test Results

Good Sensor:

Reluctor

reading is within manu-

Magnet

facturers specification
and remains steady
while sensor wires are
flexed.

Bad Sensor:

reading erratically

Black

changes as sensor wires
are flexed or display
reading is not within
manufacturers specifi­cation.

Display

Display

23

Ignition Coil Switching Action

This test checks to see if the negative
terminal of the primary ignition coil is
getting switched ON and OFF via the
ignition module and camshaft / crank­shaft position sensors. This switching
action is where the RPM or tach signal
originates. This test is primarily used for
a no start condition.

Test Procedure (see Fig. 29):

Fig. 29

Typical

Ignition

Coil

Red

Black

Ground

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Connect RED test lead to TACH
signal wire.

• If vehicle is DIS (Distributorless

Ignition System), then connect RED
test lead to the TACH signal wire
going from the DIS module to the
vehicle engine computer. (refer to

test lead jack.

vehicle service manual for location
of this wire)

• For all vehicles with distributors,
connect RED test lead to negative
side of primary ignition coil. (refer
to vehicle service manual for loca­tion of ignition coil)

4. Connect BLACK test lead to a good
vehicle ground.

5. Turn multimeter rotary switch
to correct CYLINDER selec­tion in RPM.

6. View reading on display while
engine is cranking.

• Typical cranking RPM range

is 50-275 RPM depending on
temperature, size of engine,
and battery condition.

• Refer to vehicle service

manual for specific vehicle
cranking RPM range.

7. Test Results.

Good Coil Switching Action:

Display
reading indicated a value consistent
with manufacturers specifications.

Bad Coil Switching Action:

• Display read zero RPM, meaning

the ignition coil is not being
switched ON and OFF.

• Check ignition system for wiring

defects, and test the camshaft and
crankshaft sensors.

24

Fuel System Testing

The requirements for lower vehicle emissions
has increased the need for more precise engine
fuel control. Auto manufacturers began using
electronically controlled carburetors in 1980 to
meet emission requirements. Today’s modern
vehicles use electronic fuel injection to precisely
control fuel and further lower emissions. The
digital multimeter can be used to test the fuel
mixture control solenoid on Gen­eral Motors vehicles and to mea­sure fuel injector resistance.

Typical Mixture Control

Solenoid Connection

Mixture Control

Testing GM C-3 Mixture Control Solenoid Dwell

Solenoid

This solenoid is located in the carbure­tor. Its purpose is to maintain an air/fuel
ratio of 14.7 to 1 in order to reduce
emissions. This test checks to see if the
solenoid dwell is varying.

Test Description:
This test is rather long and detailed. Refer

to vehicle service manual for the com­plete test procedure. Some important test
procedure highlights you need to pay
close attention to are listed below.

1. Make sure engine is at operating
temperature and running during
test.

2. Refer to vehicle service manual
for multimeter hook-up instruc­tions.

3. Turn multimeter rotary switch to 6
Cylinder Dwell position for all GM
vehicles.

4. Run engine at 3000 RPM.

5. Make engine run both RICH and
LEAN.

6. Watch multimeter display.

7. Multimeter display should vary
from 10° to 50° as vehicle changes
from lean to rich.

25

Measuring Fuel Injector Resistance

Fuel injectors are similar to solenoids.
They contain a coil that is switched ON
and OFF by the vehicle computer. This
test measures the resistance of this coil
to make sure it is not an open circuit.
Shorted coils can also be detected if the
specific manufacturer resistance of the
fuel injector is known.

Test Procedure (see Fig. 30):

Fig. 30

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Turn multimeter rotary switch to
200

Ω range.

Touch RED and BLACK multimeter
leads together and view reading on
display.

Display should read typically 0.2 -

1.5Ω.
If display reading was greater than

1.5Ω, check both ends of test leads
for bad connections. If bad connec­tions are found, replace test leads.

4. Disconnect wiring harness from
fuel injector - Refer to vehicle ser­vice manual for procedure.

test lead jack.

Typical Fuel

Black

Injector

5. Connect RED and BLACK test
leads across fuel injector pins.

Make sure you connect test leads
across fuel injector and not the wir­ing harness.

6. Turn multimeter rotary switch to
desired OHM range.

If the approximate resistance is
unknown, start at the largest
OHM range and decrease to the
appropriate range as required.
(see Setting the Range on page

6)

7. View reading on display ­Note range setting for cor­rect units.

Red

8. Test Results

• If display reading is 10Ω or

less, subtract test lead resis­tance found in Step 3 from
above reading.

• Compare reading to manu-

facturers specifications for
fuel injector coil resistance.

• This information is found in

vehicle service manual.

Good Fuel Injector resistance:

sistance of fuel injector coil is within
manufacturers specifications.

Bad Fuel Injector resistance:

tance of fuel injector coil is not within
manufacturers specifications.

NOTE: If resistance of fuel injector
coil is within manufacturers specifi­cations, the fuel injector could still
be defective. It is possible that the
fuel injector is clogged or dirty and
that is causing your driveability prob­lem.

Re-

Resis-

26

Testing Engine Sensors

In the early 1980’s, computer controls were installed in vehicles to meet Federal
Government regulations for lower emissions and better fuel economy. To do its job, a
computer-controlled engine uses electronic sensors to find out what is happening in
the engine. The job of the sensor is to take something the computer needs to know,
such as engine temperature, and convert it to an electrical signal which the computer
can understand. The digital multimeter is a useful tool for checking sensor operation.

Oxygen (O2) Type Sensors

The Oxygen Sensor produces a voltage
or resistance based on the amount of
oxygen in the exhaust stream. A low
voltage (high resistance) indicates a lean
exhaust (too much oxygen), while a high
voltage (low resistance) indicates a rich
exhaust (not enough oxygen). The com­puter uses this voltage to adjust the air/
fuel ratio. The two types of O
commonly in use are Zirconia and Tita­nia. Refer to illustration for appearance
differences of the two sensor types.

Test Procedure (see Fig. 31):

1. If engine is HOT, let it COOL down
before proceeding.

2. Remove Oxygen Sensor from ve­hicle.

3. Insert BLACK test lead into COM
test lead jack.

4. Insert RED test lead into

test lead jack.

Fig. 31

Sensors

2

Rich Lean

Titania-Type

Oxygen Sensor

flat element

Zirconia-Type

Oxygen Sensor

5. Test heater circuit.

• If sensor contains 3 or more wires,
then your vehicle uses a heated O
sensor.

• Refer to vehicle service manual for
location of heater pins.

• Connect RED test lead to either
heater pin.

Exposed

Flutes

2

Red

Black

Ground

1-wire or 3-wire: Ground is sensor housing
2-wire or 4-wire: Ground is in sensor wiring

harness

27

• Connect BLACK test lead to re­maining heater pin.

• Turn multimeter rotary switch to
200Ω range.

• View reading on display.

• Compare reading to manufacturer's

specification in vehicle service
manual.

• Remove both test leads from sen­sor.

6. Connect BLACK test lead to sen­sor GROUND pin.

• If sensor is 1-wire or 3-wire, then

GROUND is sensor housing.

• If sensor is 2-wire or 4-wire, then

GROUND is in sensor wiring har­ness.

• Refer to vehicle service manual for

Oxygen Sensor wiring diagram.

7. Connect RED test lead to sensor
SIGNAL pin.

8. Test Oxygen Sensor.

• Turn multimeter rotary switch to...

– 2V range for Zirconia Type Sen-

sors.
– 200KΩ range for Titania Type

Sensors.

• Light propane torch.

• Firmly grasp sensor with a pair of

locking pliers.

• Thoroughly heat sensor tip as hot

as possible, but not “glowing.” Sen­sor tip must be at 660°F to operate.

• Completely surround sensor tip

with flame to deplete sensor of
oxygen (Rich Condition).

• Multimeter display should read...
– 0.6V or greater for Zirconia Type

Sensors.
– an Ohmic(Resistance) value for

Titania Type Sensors. Reading will
vary with flame temperature.

• While still applying heat to sensor,
move flame such that oxygen can
reach sensor tip (Lean Condition).

• Multimeter display should read...
– 0.4V or less for Zirconia Type

Sensors.
– an overrange condition for Tita-

nia Type Sensors. (See Setting the
Range on page 6.)

9. Repeat Step 8 a few times to verify
results.

10.Extinguish Flame, let sensor cool,
and remove test leads.

11.Test Results.

Good Sensor:

• Heater Circuit resistance is within

manufacturer's specification.

• Oxygen Sensor output signal

changed when exposed to a rich
and lean condition.

Bad Sensor:

• Heater Circuit resistance is not

within manufacturer's specification.

• Oxygen Sensor output signal did

not change when exposed to a rich
and lean condition.

• Oxygen sensor output voltage

takes longer than 3 seconds to
switch from a rich to a lean condi­tion.

28

Temperature Type Sensors

A temperature sensor is a thermistor or
a resistor whose resistance changes with
temperature. The hotter the sensor gets,
the lower the resistance becomes. Typi­cal thermistor applications are engine
coolant sensors, intake air temperature
sensors, transmission fluid temperature
sensors, and oil temperature sensors.

Test Procedure (see Fig. 32):

Fig. 32

1. If engine is HOT let it COOL down
before proceeding.

Make sure all engine and transmis­sion fluids are at outside air tem­perature before proceeding with this
test!

2. Insert BLACK test lead into COM
test lead jack.

3. Insert RED test lead into

4. Disconnect wiring harness from
sensor.

5. If testing Intake Air Temperature
Sensor - Remove it from vehicle.

All other temperature sensors can
remain on vehicle for testing.

6. Connect RED test lead to either
sensor pin.

7. Connect BLACK test lead to re­maining sensor pin.

8. Turn multimeter rotary switch to
desired OHM range.

If the approximate resistance is un­known, start at the largest OHM
range and decrease to the appropri­ate range as required. (See Setting
the Range on page 6)

Hair Dryer

Temperature

Red

test lead jack.

Typical

Intake Air

Sensor

Black

9. View and record reading on dis­play.

10.Disconnect multimeter test leads
from sensor and reconnect sen­sor wiring.

This step does not apply to intake air
temperature sensors. For intake air
temperature sensors, leave multim­eter test leads still connected to sen­sor.

11.Heat up sensor.

If testing Intake Air Temperature Sen­sor:

• To heat up sensor dip sensor tip

into boiling water, or...

• Heat tip with a

lighter if sensor tip is
metal or a hair dryer if sensor tip is
plastic.

• View and record smallest reading
on display as sensor is heated.

• You may need to decrease the
range to get a more accurate read­ing.

For all other temperature sensors:

• Start engine and let idle until upper
radiator hose is warm.

• Turn ignition key OFF.

• Disconnect sensor wiring harness

and reconnect multimeter test
leads.

• View and record reading on dis­play.

12.Test Results.

Good Sensor:

• Temperature sensors HOT resis­tance is at least 300Ω less than its
COLD resistance.

• The key point is that the COLD re­sistance decreases with increasing
temperature.

Bad Sensor:

• There is no change between the
temperature sensors HOT resis­tance from the COLD resistance.

• The temperature sensor is an open
or a short circuit.

29

Position Type Sensors

Position sensors are potentiometers or
a type of variable resistor. They are
used by the computer to determine po­sition and direction of movement of a
mechanical device. Typical position sen­sor applications are throttle position
sensors, EGR valve position sensors,
and vane air flow sensors.

Test Procedure (see Fig. 33):

Fig. 33

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Disconnect wiring harness from
sensor.

4. Connect Test Leads.

• Connect RED test lead to sensor

POWER pin.

• Connect BLACK test lead to sen-

sor GROUND pin.

• Refer to vehicle service manual for

location of sensor POWER and
GROUND pins.

5. Turn multimeter rotary switch to
20K

Ω range.

6. View and record reading on dis­play.

• Display should read some resis-

tance value.

• If multimeter is overranging, adjust

the range accordingly. (See Set­ting the Range on page 6.)

Typical Toyota Throttle

Position Sensor

Red

POWER GROUND

SIGNAL IDLE SWITCH

test lead jack.

• If multimeter overranges on larg­est range, then sensor is an open
circuit and is defective.

7. Move RED test lead to sensor SIG­NAL pin.

• Refer to vehicle service manual for

location of sensor SIGNAL pin.

8. Operate Sensor.

Throttle Position Sensor:

• Slowly move throttle linkage
from closed to wide open posi­tion.

• Depending on hook-up, the dis­play reading will either

Black

or decrease in resistance.

• The display reading should ei-
ther

start at or end at the ap­proximate resistance value
measured in Step 6.

• Some throttle position sensors
have an Idle or Wide Open
Throttle (WOT) switch in addi­tion to a potentiometer.

• To test these switches, follow the
Testing Switches test procedure
on page 13.

• When you are told to operate
switch, then move throttle linkage.

Vane Air Flow Sensor:

• Slowly open vane “door” from
closed to open by pushing on it
with a pencil or similar object. This
will not harm sensor.

• Depending on hook-up, the dis­play reading will either

increase or

decrease in resistance.

• The display reading should either
start at or end at the approximate
resistance value measured in Step

6.

• Some vane air flow sensors have
an idle switch and an intake air
temperature sensor in addition to a
potentiometer.

• To test idle switch see Testing
Switches on page 13.

• When you are told to operate
switch, then open vane “door”.

30

increase

• To test intake air tempera­ture sensor see Temperature
Type Sensors on page 29.

EGR Valve Position

Frequency
Only

• Remove vacuum hose from
EGR valve.

• Connect hand vacuum pump
to EGR valve.

• Gradually apply vacuum to
slowly open valve. (Typi­cally, 5 to 10 in. of vacuum
fully opens valve.)

• Depending on hook-up, the
display reading will either
increase or decrease in re­sistance.

• The display reading should
either

start at or end at the
approximate resistance
value measured in Step 6.

9. Test Results.

Good Sensor:

Display
reading gradually increases
or decreases in resistance as
sensor is opened and closed.

Bad Sensor:

There is no
change in resistance as sen­sor is opened or closed.

Manifold Absolute
Pressure (MAP) and
Barometric Pressure
(BARO) Sensors

This sensor sends a signal to the com­puter indicating atmospheric pressure
and/or engine vacuum. Depending on
the type of MAP sensor, the signal may
be a dc voltage or a frequency. GM,
Chrysler, Honda and Toyota use a dc
voltage MAP sensor, while Ford uses a
frequency type. For other manufactur­ers refer to vehicle service manual for
type of MAP sensor used.

Test Procedure (see Fig. 34):

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

test lead jack.

Fig. 34

Ground

Black

Red

Typical

GM

MAP

Sensor

Computer

3. Disconnect wiring harnc Û and
vacuum line from MAP sensor.

4. Connect jumper wire between Pin
A on wiring harness and sensor.

5. Connect another jumper wire be­tween Pin C on wiring harness
and sensor.

6. Connect RED test lead to sensor
Pin B.

7. Connect BLACK test lead to good
vehicle ground.

8. Make sure test leads and jumper
wires are not touching each other.

9. Connect a hand held vacuum
pump to vacuum port on MAP sen­sor.

10. Turn Ignition Key ON, but do not
start engine!

11.Turn multimeter rotary switch to...

• 20V range for DC type MAP sen-

sors.

• 4 Cylinder RPM position for Fre-

quency type MAP sensors.

31

DC
Only

To

12.View reading on display.

DC Volts Type Sensor:

• Verify hand held vacuum pump is
at 0 in. of vacuum.

• Display reading should be approxi­mately 3V or 5V depending on
MAP sensor manufacturer.

Frequency Type Sensor:

• Verify hand held vacuum pump is
at 0 in. of vacuum.

• Display reading should be approxi­mately 4770RPM ± 5% for Ford
MAP sensors only.

• For other frequency type MAP sen­sors refer to vehicle service manual
for MAP sensor specifications.

• It is O.K. if last two display digits
change

slightly while vacuum is

held constant.

• Remember to multiply display
reading by 10 to get actual RPM.

• To convert RPM to Frequency or
vice versa, use equation below.

Frequency =

RPM

30

(Equation Only Valid for Multimeter
in 4 Cylinder RPM Position)

13.Operate Sensor.

• Slowly apply vacuum to MAP sen­sor - Never exceed 20 in. of vacuum
because damage to MAP sensor
may result.

• Display reading should decrease
in

voltage or RPM as vacuum to

MAP sensor is increased.

• Refer to vehicle service manual
for charts relating voltage and fre­quency drop to increasing engine
vacuum.

• Use equation above for Frequency
and RPM conversions.

14.Test Results.

Good Sensor:

• Sensor output voltage or
frequency(RPM) are within manu­facturers specifications at 0 in. of
vacuum.

• Sensor output voltage or frequency
(RPM) decrease with increasing
vacuum.

Bad Sensor:

• Sensor output voltage or frequency
(RPM) are not within manufactur­ers specifications at 0 in. of
vacuum.

• Sensor output voltage or frequency
(RPM) do not change with increas­ing vacuum.

Mass Air Flow (MAF)
Sensors

This sensor sends a signal to the com­puter indicating the amount of air enter­ing the engine. Depending on the sen­sor design, the signal may be a dc volt­age, low frequency, or high frequency
type. The CP7677 can only test the

voltage

and

MAF sensors. The high frequency type

sensors output a frequency that is too
high for the CP7677 to measure. The
high frequency type MAF is a 3-pin sen­sor used on 1989 and newer GM ve­hicles. Refer to vehicle service manual
for the type of MAF sensor your vehicle
uses.

Test Procedure (see Fig. 35):

1. Insert BLACK test lead into COM
test lead jack.

2. Insert RED test lead into

3. Connect BLACK test lead to good
vehicle ground.

4. Connect RED test lead to MAF
signal wire.

• Refer to vehicle service manual for

• You may have to backprobe or

• Refer to vehicle service manual for

5. Turn Ignition Key ON, but do not
start engine!

6. Turn multimeter rotary switch to...

32

low frequency type

test lead jack.

location of MAF signal wire.

pierce MAF signal wire in order to
make connection.

best way to connect to MAF signal
wire.

dc

of

Fig. 35

Frequency
Only

Ground

Black

Red

Typical GM 1988 & older

Low Frequency type

MAF Sensor

• 20V range for DC type MAF sen­sors.

• 4 Cylinder RPM position for Low
Frequency type MAF sensors.

7. View reading on display.

DC Volts Type Sensor:

• Display reading should be approxi­mately 1V or less depending on
MAF sensor manufacturer.

Low Frequency Type Sensor:

• Display reading should be approxi­mately 330RPM ± 5% for GM Low
Frequency MAF sensors.

• For other Low Frequency type MAF
sensors refer to vehicle service
manual for MAF sensor specifications.

• It is O.K. if last two display digits
change slightly while Key is ON.

• Remember to multiply display read­ing by 10 to get actual RPM.

• To convert RPM to Frequency or
vice versa, use equation below.

Frequency =

{Equation Only Valid for Multim­eter in 4 Cylinder RPM Position}

RPM

30

DC
Only

8. Operate Sensor.

• Start engine and let idle.

• Display reading should...

- increase in
Key On Engine OFF for DC
type MAF sensors.

- increase in
On Engine OFF for Low Fre­quency type MAF sensors.

• Rev Engine.

• Display reading should...

- increase in
for DC type MAF sensors.

- increase in
for Low Frequency type MAF
sensors.

• Refer to vehicle service
manual for charts relating
MAF sensor voltage or fre­quency (RPM) to increasing
air flow.

• Use equation above for Fre­quency and RPM conver­sions.

9. Test Results.

Good Sensor:

• Sensor output voltage or frequency
(RPM) are within manufacturers
specifications at Key ON Engine
OFF.

• Sensor output voltage or frequency
(RPM) increase with increasing air
flow.

Bad Sensor:

• Sensor output voltage or frequency
(RPM) are not within manufactur­ers specifications at Key ON En­gine OFF.

• Sensor output voltage or frequency
(RPM) do not change with increas­ing air flow.

33

voltage from

RPM from Key

voltage from Idle

RPM from Idle

Electrical Specifications

DC Volts

Range: 200mV, 2V, 20V, 200V
Accuracy : ±(0.5% rdg + 5 dgts)

Range: 1000V
Accuracy: ±(0.8% rdg + 5 dgts)

AC Volts

Range: 2V, 20V, 200V
Accuracy : ±(0.8% rdg + 5 dgts)

Range: 750V
Accuracy: ±(1.0% rdg + 4 dgts)

DC Current

Range: 200mA
Accuracy: ±(0.8% rdg + 5 dgts)

Range: 10A
Accuracy: ±(1.2% rdg + 5 dgts)

Resistance

Range: 200Ω, 2KΩ, 20KΩ, 200KΩ, 2MΩ
Accuracy: ±(0.8% rdg + 5 dgts)

Range: 20MΩ
Accuracy: ±(1.5% rdg + 5 dgts)

Dwell

Range: 4CYL, 6CYL, 8CYL
Accuracy: ±(3.0% rdg + 5 dgts)

RPM

Range: 4CYL, 6CYL, 8CYL
Accuracy: ±(3.0% rdg + 5 dgts)

Audible Continuity

Buzzer sounds at approximately less
than 30-50 Ohms.

34