JA VEHICLE SPEED CONTROL SYSTEM 8H - 1
VEHICLE SPEED CONTROL SYSTEM
CONTENTS
page page
DESCRIPTION AND OPERATION
AUTOMATIC SPEED CONTROL OVERSPEED
REDUCTION ........................... 3
POWERTRAIN CONTROL MODULE .......... 3
SERVO CABLE .......................... 3
SPEED CONTROL SERVO .................. 2
SPEED CONTROL SWITCHES .............. 3
SPEED CONTROL SYSTEM ................ 1
STOP LAMP SWITCH ..................... 3
VACUUM RESERVOIR .................... 3
VEHICLE SPEED AND DISTANCE ............ 3
DIAGNOSIS AND TESTING
CHECKING FOR DIAGNOSTIC CODES ........ 4
ELECTRICAL TESTS AT POWERTRAIN
CONTROL MODULE ..................... 6
DESCRIPTION AND OPERATION
SPEED CONTROL SYSTEM
DESCRIPTION
The speed control system is electronically con-
trolled and vacuum operated. The electronic control
is integrated into the Powertrain Control Module,
located on the left side of the engine compartment
next to the air cleaner. The controls are located on
the steering wheel and consist of two switches. The
ON, OFF, RESUME, ACCEL, SET, COAST, and
CANCEL, buttons are located on a spoke of the steering wheel (Fig. 1). For identification and location of
the major components (Fig. 2).
The system is designed to operate at speeds above
30 mph (50 km/h).
OVERSHOOT/UNDERSHOOT FOLLOWING
SPEED CONTROL SET ................... 5
ROAD TEST ............................ 4
SERVO VACUUM TEST .................... 5
SPEED CONTROL ELECTRICAL TEST ........ 4
SPEED CONTROL SWITCH TEST ............ 5
STOP LAMP SWITCH TEST ................ 5
VACUUM SUPPLY TEST ................... 7
VEHICLE SPEED SIGNAL .................. 7
REMOVAL AND INSTALLATION
SERVO ................................ 7
SPEED CONTROL SERVO CABLE ............ 8
SPEED CONTROL SWITCH ................. 8
STOP LAMP SWITCH .................... 8
VACUUM RESERVOIR .................... 9
WARNING: THE USE OF SPEED CONTROL IS NOT
RECOMMENDED WHEN DRIVING CONDITIONS DO
NOT PERMIT MAINTAINING A CONSTANT SPEED,
SUCH AS IN HEAVY TRAFFIC OR ON ROADS THAT
ARE WINDING, ICY, SNOW COVERED, OR SLIPPERY.
OPERATION
When speed control is selected by depressing the
ON switch, the PCM allows a set speed to be stored
in RAM for speed control. To store a set speed,
Fig. 1 Speed Control Switch
depress the SET switch while the vehicle is moving
at a speed between 30 and 85 mph. In order for the
speed control to engage, the brakes cannot be
applied, nor can the gear selector be indicating the
transmission is in Park or Neutral.
The speed control can be disengaged manually by:
• Stepping on the brake pedal
8H - 2 VEHICLE SPEED CONTROL SYSTEM JA
DESCRIPTION AND OPERATION (Continued)
Fig. 2 Speed Control System
• Depressing the OFF switch
• Depressing the CANCEL switch.
• Depressing the clutch pedal
NOTE: Depressing the OFF switch or turning off
the ignition switch will erase the set speed stored
in the PCM.
For added safety, the speed control system is programmed to disengaged for any of the following conditions:
• An indication of Park or Neutral
• An rapid increase rpm (indicates that the clutch
has been disengaged)
• Excessive engine rpm (indicates that the trans-
mission may be in a low gear)
• The speed signal increases at a rate of 10 mph
per second (indicates that the co-efficient of friction
between the road surface and tires is extremely low)
• The speed signal decreases at a rate of 10 mph
per second (indicates that the vehicle may have
decelerated at an extremely high rate)
Once the speed control has been disengaged,
depressing the RESUME switch when speed is
greater than 25 mph restores the vehicle to the target speed that was stored in the PCM.
While the speed control is engaged, the driver can
increase the vehicle speed by depressing the ACCEL
switch. The new target speed is stored in the PCM
when the ACCEL is released. The PCM also has a
9tap-up9 feature in which vehicle speed increases at a
rate of approximately 2 mph for each momentary
switch activation of the ACCEL switch. The PCM
also provides a means to decelerate without disengaging speed control. To decelerate from an existing
recorded target speed, depress and hold the COAST
switch until the desired speed is reached, then
release the switch.
SPEED CONTROL SERVO
DESCRIPTION
The servo unit consists of a solenoid valve body,
and a vacuum chamber.
OPERATION
The PCM controls the solenoid valve body. The
solenoid valve body controls the application and
release of vacuum to the diaphragm of the vacuum
servo. The servo unit cannot be repaired and is serviced only as a complete assembly.
JA VEHICLE SPEED CONTROL SYSTEM 8H - 3
DESCRIPTION AND OPERATION (Continued)
SPEED CONTROL SWITCHES
DESCRIPTION
There are two separate switch pods that operate
the speed control system.
OPERATION
The steering-wheel-mounted switches use multiplexed circuits to provide inputs to the PCM for ON,
OFF, RESUME, ACCELERATE, SET, DECEL and
CANCEL modes. Refer to the owner’s manual for
more information on speed control switch functions
and setting procedures.
The individual switches cannot be repaired. If one
switch fails, the entire switch module must be
replaced.
AUTOMATIC SPEED CONTROL OVERSPEED REDUCTION
OPERATION
Transmission control software includes an automatic speed control overspeed reduction feature. This
maintains vehicle speed at the selected set point
when descending a grade.
The Transmission Control Module (TCM) first
senses that the speed control is set. If the set speed
is exceeded by more than 4 mph (6.5 km/hr) and the
throttle is closed, the TCM causes the transaxle to
downshift to THIRD gear. After downshifting, the
automatic speed control resumes normal operation.
To ensure that an upshift is appropriate after the set
speed is reached, the TCM waits until the speed control system opens the throttle at least 6 degrees
before upshifting to OVERDRIVE again.
If the driver applies the brakes, canceling automatic speed control operation with the transaxle still
in THIRD gear, the TCM maintains this gear until
the driver opens the throttle at least 6 degrees to
avoid an inappropriate upshift. The upshift is also
delayed for 2.5 seconds after reaching the 6 degrees
throttle opening in anticipation that the driver might
open the throttle enough to require THIRD gear.
This will avoid unnecessary and disturbing transmission cycling. If the automatic speed control RESUME
feature is used after braking, the upshift is delayed
until the set speed is achieved to reduce cycling and
provide better response.
STOP LAMP SWITCH
DESCRIPTION
The switch is mounted on the brake pedal mounting bracket under the instrument panel.
OPERATION
Vehicles equipped with the speed control option use
a dual function stop lamp switch. The PCM monitors
the state of the dual function stop lamp switch. Refer
to the Brake section for more information on stop
lamp switch service and adjustment procedures.
SERVO CABLE
DESCRIPTION
The speed control servo cable is connected between
the speed control vacuum servo diaphragm and the
throttle body control linkage.
OPERATION
This cable causes the throttle control linkage to
open or close the throttle valve in response to movement of the vacuum servo diaphragm.
POWERTRAIN CONTROL MODULE
OPERATION
The speed control electronic control circuitry is
integrated into the Powertrain Control Module
(PCM). The PCM is located in the engine compartment. The PCM speed control functions are monitored by the On-Board Diagnostics (OBD). All OBDsensed systems are monitored by the PCM. Each
monitored circuit is assigned a Diagnostic Trouble
Code (DTC). The PCM will store a DTC in electronic
memory for any failure it detects. The PCM cannot
be repaired and must be replaced if faulty.
USE THE DRB SCAN TOOL TO REPROGRAM
THE NEW PCM WITH THE VEHICLES ORIGINAL IDENTIFICATION NUMBER (VIN) AND
THE VEHICLES ORIGINAL MILEAGE. IF THIS
STEP IS NOT DONE A DIAGNOSTIC TROUBLE
CODE (DTC) MAY BE SET.
VACUUM RESERVOIR
OPERATION
The reservoir contains a one-way check valve to
trap engine vacuum in the reservoir. When engine
vacuum drops, as in climbing a grade while driving,
the reservoir supplies the vacuum needed to maintain proper speed control operation. The vacuum reservoir cannot be repaired and must be replaced if
faulty.
VEHICLE SPEED AND DISTANCE
OPERATION
The 4 speed automatic Transmission Control Module (TCM) supplies the speed input to the PCM. The
PCM determines acceleration rates. The speed con-
8H - 4 VEHICLE SPEED CONTROL SYSTEM JA
DESCRIPTION AND OPERATION (Continued)
trol software in the PCM uses vehicle speed and
acceleration to control to the set speed.
Vehicles with a 3 speed automatic or manual transmission have a Vehicle Speed Sensor (VSS) mounted
to an adapter near the transmission output shaft.
The sensor is driven through the adapter by a speedometer pinion gear. The VSS pulse signal is monitored by the PCM to determine vehicle speed and to
maintain speed control set speed. Refer to the appropriate Powertrain Diagnostic Procedures manual for
diagnosis and testing of this component.
DIAGNOSIS AND TESTING
ROAD TEST
Perform a vehicle road test to verify reports of
speed control system malfunction. The road test
should include attention to the speedometer. Speedometer operation should be smooth and without flutter at all speeds.
Flutter in the speedometer indicates a problem
which might cause surging in the speed control system. The cause of any speedometer problems should
be corrected before proceeding. Refer to the Instrument Panel and Gauges for speedometer diagnosis.
If a road test verifies a surge following a set and
the speedometer operates properly see “Overshoot/
Undershoot on speed control set”.
If a road test verifies an inoperative system, and
the speedometer operates properly, check for:
• A Diagnostic Trouble Code (DTC). If a DTC
exists, conduct tests per the Powertrain Diagnostic
Procedures service manual.
• A misadjusted brake (stop) lamp switch. This
could also cause an intermittent problem.
• Loose or corroded electrical connections at the
servo. Corrosion should be removed from electrical
terminals and a light coating of Mopar Multipurpose
Grease, or equivalent, applied.
• Leaking vacuum reservoir.
• Loose or leaking vacuum hoses or connections.
• Defective one-way vacuum check valve.
• Secure attachment at both ends of the speed
control servo cable.
• Smooth operation of throttle linkage and throttle
body air valve.
• Conduct electrical test at PCM.
• Failed speed control servo. Do the servo vacuum
test.
CAUTION: When test probing for voltage or continuity at electrical connectors, care must be taken
not to damage connector, terminals or seals. If
these components are damaged, intermittent or
complete system failure may occur.
CHECKING FOR DIAGNOSTIC CODES
When trying to verify a speed control system electronic malfunction: Connect a DRB scan tool if available to the data link connector. The connector is
located at left side of the steering column, and at
lower edge of the panel.
(1) A speed control malfunction may occur without
a diagnostic code being indicated.
For further information and usage of the DRB scan
tool and a more complete list of Diagnostic Trouble
Code and No Trouble Codes, refer to the Powertrain
Diagnostic Manual.
SPEED CONTROL SLOWS DOWN BY ITSELF
Test the vehicle speed sensor/output speed sensor.
If sensor fails replace sensor, if it passes perform the
following test:
(1) Check for transmission DTC.
(2) Perform the speed control switch test on the
DECEL switch, if it fails replace switch.
(3) If the switch passes, conduct the vacuum supply test.
(4) If it passes, conduct the servo vacuum test. If it
fails replace servo.
(5) If continuity, replace the PCM.
SPEED CONTROL ELECTRICAL TEST
Electronic speed control systems may be tested
using two different methods. One involves use of a
DRB. If this test method is desired, refer to the Powertrain Diagnostic Test Procedures for charging and
speed control system manual.
The other test method uses a volt/ohm meter. The
volt/ohm meter method is described in the following
tests.
If any information is needed concerning wiring,
refer to Group 8W, Wiring Diagrams.
CAUTION: When test probing for voltage or continuity at electrical connectors, care must be taken
not to damage connector, terminals, or seals. If
these components are damaged, intermittent or
complete system failure may occur.
When electrical connections are removed, corrosion
should be removed from electrical terminals and a
light coating of Mopar Multi-Purpose Grease, or
equivalent, applied. Inspect connectors for damage
terminals.
A poor connection can cause a complete or intermittent malfunction and is also the only connection
in the circuit, that can not be tested. For this reason,
a loose connection may be misdiagnosed as a component malfunction.
JA VEHICLE SPEED CONTROL SYSTEM 8H - 5
DIAGNOSIS AND TESTING (Continued)
OVERSHOOT/UNDERSHOOT FOLLOWING SPEED CONTROL SET
If the operator repeatedly presses and releases the
set button with their foot off of the accelerator (a “lift
foot set” to begin speed control operation), the vehicle
may accelerate and exceed the desired set speed by
up to 5 MPH (8 km/h) and then decelerate to less
than the desired set speed before finally achieving
the desired set speed.
The Speed Control has an adaptive strategy that
compensates for vehicle-to-vehicle variations in speed
control cable lengths. When the speed control is set
with the vehicle operators foot off of the accelerator
pedal, the speed control thinks there is excessive
speed control cable slack and adapts. If the lift foot
sets are continually used, the speed control overshoot/undershoot condition will develop.
To “unlearn” the overshoot/undershoot condition,
the vehicle operator has to press and release the set
button while maintaining the desired set speed with
the accelerator pedal (not decelerating or accelerating), and then turn the cruise control switch to the
OFF position (or press the CANCEL button if
equipped) after waiting 10 seconds. This procedure
must be performed approximately 10–15 times to
completely unlearn the overshoot/undershoot condition.
SERVO VACUUM TEST
(1) Turn ignition switch to the ON position without starting engine. Activate speed control ON
switch.
(2) Disconnect the four-way electrical connector
and the vacuum harness at the servo (Fig. 3).
(3) Connect a jumper wire from Pin 3 of the servo
to Pin 3 of the wire connector.
(4) Ground Pins 2 and 4 in the servo. Do not connect pin 1.
(5) Connect a hand held vacuum pump to the vacuum nipple and apply 10 - 15 inches of vacuum.
(6) If servo pulls cable, replace servo.
(7) Ground Pin 1 on servo.
(8) Check that the throttle cable pulls in and holds
as long as the vacuum pump is connected. After one
minute, check if cable is still holding. If cable does
not hold replace the servo.
(9) Disconnect jumper from pin 3. Cable should
return to rest position. If not, replace servo.
(10) Connect 4 way electrical connector and vacuum harness to servo.
SPEED CONTROL SWITCH TEST
Refer to the appropriate Powertrain Diagnostic
Manual for switch test values.
STOP LAMP SWITCH TEST
(1) Remove the stop lamp switch refer to Stop
Switch Removal/Installation in this section. Disconnect connector from stop lamp switch (Fig. 4). Using
an ohmmeter, switch continuity may be checked as
follows:
Fig. 3 Servo Harness Connector
Fig. 4 Stop Lamp Wiring
8H - 6 VEHICLE SPEED CONTROL SYSTEM JA
DIAGNOSIS AND TESTING (Continued)
(2) With switch plunger released, there should be
continuity between Pin 5 and Pin 6.
(3) With switch plunger depressed, there should be
continuity:
• Between Pin 1 and Pin 2.
• Between Pin 3 and Pin 4.
(4) If the above results are not obtained, the stop
lamp switch is defective or out of adjustment.
(5) Stop lamp switch adjustment is detailed in the
Brake section.
ELECTRICAL TESTS AT POWERTRAIN CONTROL MODULE
(1) Unplug the GRAY 40-way connector from the
Powertrain Control Module (PCM), (Fig. 5).
Fig. 5 Powertrain Control Module Location
(2) Remove both steering wheel speed control
switches and disconnect the wire connectors.
(a) Using an ohmmeter, check for continuity
between cavity 41 of the PCM connector and cavity
1 of each speed control switch connector (Fig. 6).
(b) If no continuity, repair as necessary.
(c) Using an ohmmeter, check for continuity
between cavity 41 of the PCM connector and
ground.
(d) If continuity, repair as necessary.
(e) If no continuity, perform the Switch Test.
(f) Plug GRAY 40 way connector into PCM.
(g) Plug switch connectors back into switches.
(3) Unplug speed control servo electrical connector.
(4) Place ignition switch in the ON position and
turn on the speed control system, for the following
tests.
(a) Using a voltmeter, measure voltage from cavity 3 of servo connector to ground. Voltmeter
Fig. 6 PCM 40—Way Connectors
should read ignition voltage. If voltage is low, skip
to Step 7.
(b) Turn speed control and ignition switch OFF.
Using an ohmmeter, place positive lead on pin 3
and negative lead on pin 4 on the speed control
servo. Check continuity from pin 3 to pin 4.
(c) If no continuity, replace the speed control
servo. If continuity is greater than 49 ohms, clean
terminals.
(d) Using an ohmmeter, place positive lead on
pin 3 and negative lead on pin 2 on the speed control servo. Check continuity from pin 3 to pin 2.
(e) If no continuity, replace the speed control
servo. If continuity is greater than 49 ohms, clean
terminals.
(f) Using an ohmmeter, place positive lead on
pin 3 and negative lead on pin 1 on the speed control servo. Check continuity from pin 3 to pin 1.
(g) If no continuity, replace the speed control
servo. If continuity is greater than 49 ohms, clean
terminals.
(h) Using an ohmmeter at the servo connector,
place positive lead on cavity 4 and negative lead on
ground. Check continuity from cavity 4 to ground.
If no continuity, repair open circuit
(i) Unplug 2 40-way PCM connectors
(j) Using an ohmmeter, check continuity from
cavity 1 of servo connector to cavity 56 on PCM
connector. If no continuity, repair open circuit
(k) Using an ohmmeter, check continuity from
cavity 1 of servo connector to ground. If continuity,
repair as necessary.
(l) If continuity is OK, check continuity from
cavity 2 of servo connector to cavity 80 of PCM
connector. If no continuity, repair open circuit
(m) Using an ohmmeter, check continuity from
cavity 2 of servo connector to ground. If continuity,
repair as necessary.
(n) Using an ohmmeter, check continuity from
cavity 1 of servo connector to cavity 2 of servo connector. If continuity, repair as necessary.
(o) Reconnect the 4 way connector to servo.
JA VEHICLE SPEED CONTROL SYSTEM 8H - 7
DIAGNOSIS AND TESTING (Continued)
(5) Using an ohmmeter, check continuity from cavity 62 of the PCM connector to ground. If continuity
is OK with brake pedal in unpressed position, proceed to Step 6.
(a) If no continuity, perform the Stop Lamp
switch test. Replace or adjust switch as required.
(b) If switch passes test, check continuity from
cavity 62 of the PCM connector to cavity 1 of the
stop lamp switch connector. Repair open circuit as
required.
(c) If continuity is OK between cavity 62 and
cavity 1, repair open circuit between cavity 2 of the
stop lamp switch connector and ground.
(6) Using an ohmmeter, check continuity from cav-
ity 76 on PCM connector to ground with the transmission in park or neutral. If no continuity, test TRS/
Park-Neutral switch and switch wiring
(7) Turn speed control and ignition switch OFF.
(8) Unplug the BLACK 40-way connector from the
Powertrain Control Module (PCM)
(9) Using an ohmmeter, check continuity from cav-
ity 3 of servo connector to cavity 5 on the PCM connector.
(a) If continuity is OK, replace PCM. Check circuit for short to ground before replacing PCM.
(b) If no continuity, remove stop lamp switch
and conduct Stop Lamp Switch Test. If test fails,
adjust or replace as necessary.
(c) If switch passes, measure continuity from
cavity 4 of stop lamp switch connector to cavity 3
of servo connector. Repair open circuit if necessary.
(d) If continuity is OK, measure continuity from
cavity 3 of stop lamp switch to cavity 5 of PCM
connector. Repair open circuit as necessary.
(e) Install PCM connectors onto PCM and speed
control servo connector to servo.
VACUUM SUPPLY TEST
(1) Disconnect vacuum hose at the servo and
install a vacuum gauge in the hose (Fig. 7).
(2) Start engine and observe gauge at idle. Vac-
uum gauge should read at least ten inches of mercury. Shut off engine, the vacuum should continue to
hold 10 inches of mercury.
(3) If vacuum does not meet this requirement,
check and correct the following vacuum leaks in the
vacuum lines, check valve, vacuum reservoir or poor
engine performance.
VEHICLE SPEED SIGNAL
For diagnosis and testing of the Vehicle Speed Signal (VSS), refer to the appropriate Powertrain Diagnostic Procedures service manual. Also refer to the
DRB scan tool.
REMOVAL AND INSTALLATION
SERVO
REMOVAL
(1) Remove two nuts attaching speed control cable
and mounting bracket to servo.
(2) Remove servo from the mounting bracket.
(3) Disconnect electrical connectors and vacuum
hose.
(4) Remove cable from thottle cam. Refer to Speed
Control Servo Cable Removal/Installation in this section.
(5) Remove clip attaching cable to servo.
Fig. 7 Vacuum Gauge Test
8H - 8 VEHICLE SPEED CONTROL SYSTEM JA
REMOVAL AND INSTALLATION (Continued)
INSTALLATION
(1) Install servo cable to servo and install clip.
(2) Install speed control cable to throttle cam.
(3) Connect vacuum hose to servo.
(4) Connect electrical connector.
(5) Insert servo studs through holes in speed con-
trol cable and mounting bracket.
(6) Install nuts, tighten to 7 N·m (60 in. lbs.).
SPEED CONTROL SWITCH
The speed control switches are mounted in the
steering wheel and wired through the clock spring
device under the airbag module (Fig. 1).
WARNING: IF REMOVAL OF AIRBAG MODULE IS
NECESSARY, REFER TO THE RESTRAINT SYSTEMS.
REMOVAL
(1) Turn off ignition.
(2) Remove two screws from side of each switch.
(3) Rock switch away from airbag and steering
wheel.
(4) Disconnect two-way electrical connector.
(5) Repeat for the other switch.
INSTALLATION
(1) Install switches.
(2) Connect two-way electrical connector.
(3) Install two screws to the side of each switch.
(4) Install airbag, refer to the Restraint Systems
STOP LAMP SWITCH
REMOVAL
Remove the switch from the bracket by depressing
the brake pedal and rotating the switch in a counterclockwise direction approximately 30 degrees. Pull
the switch rearward and remove from bracket. Disconnect wiring harness connector.
INSTALLATION
Before installing the switch, reset the adjustable
switch plunger by pulling on the plunger head until
the plunger reaches the end of its travel. A ratcheting sound will be heard during this procedure.
Connect the wiring harness to the switch. Mount
the switch into the bracket by holding the switch
with the plunger facing forward in car. There is an
index key on the switch that mates with the bracket
slot at the top of the square hole. Align key and push
switch into square hole in bracket while depressing
the brake pedal. Once the switch is seated in the
hole, rotate clockwise approximately 30 degrees to
lock into place. The switch will automatically adjust
when the pedal is released. Pull back on the pedal to
assure correct adjustment.
SPEED CONTROL SERVO CABLE
REMOVAL
(1) Remove throttle control shield, if equipped (Fig.
8).
(2) Remove throttle cable clasp from the throttle
body cam.
(3) Remove speed control cable from throttle cam
by sliding clasp out hole used for throttle cable.
(4) Compress the retaining tabs on the cable and
slide cable out of bracket.
(5) Remove 2 nuts retaining bracket to servo.
(6) Remove retaining clip holding cable to servo.
INSTALLATION
(1) Install retaining clip to cable at servo.
(2) Slide cable bell housing over servo mounting
studs.
(3) Install 2 nuts at cable to servo and servo
bracket, tighten to 7 N·m (60 ins. lbs.).
(4) Slide cable into throttle cable bracket and
engage retaining tabs.
(5) Rotate the throttle cam forward to the wide
open position and install speed control cable clasp.
JA VEHICLE SPEED CONTROL SYSTEM 8H - 9
REMOVAL AND INSTALLATION (Continued)
(6) Rotate the throttle cam forward to the wide
open position and install throttle cable clasp.
(7) Install throttle control shield, if equipped.
Fig. 9 Disconnecting Throttle Cable—Typical
REMOVAL
(1) 2.5L ONLY Remove the intake manifold, refer
to the Engine section.
(2) Disconnect vacuum hoses from reservoir.
(3) Pull vacuum reservoir from dash panel.
Fig. 8 Throttle Control Shield
VACUUM RESERVOIR
The vacuum reservoir is located on the dash panel
next to the brake booster.
INSTALLATION
(1) Push reservoir onto dash panel.
(2) Connect hoses to reservoir.
(3) 2.5L ONLY Install intake manifold, refer to
the Engine section.
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