CRUISE CONTROL SYSTEM

1988 Jeep Cherokee

1988 Cruise Control Systems JEEP CRUISE COMMAND

All Models

DESCRIPTION & OPERATION

Jeep vehicles use an electro-mechanical servo system. The system consists of a control module, speed sensor, servo, control switch assembly, vacuum storage canister, check valve and release system. Release system consists of a mechanical vacuum vent valve and brake and clutch (M/T) release switches.

Cruise control switch is an integral part of turn signal switch lever and consists of 2 separate switches. First is an "ON-OFF" and "RESUME" slide switch located on flat of directional switch lever.

Second is "SET/COAST" push button switch located at end of directional switch lever. To engage system, move slide switch to "ON" position and accelerate to desired speed. Depress and release "SET/COAST" button on end of switch lever. System will now maintain selected speed.

System will automatically disengage when brake or clutch pedal is depressed. It can be re-engaged to previously selected speed by accelerating to 30 MPH and moving slide switch to "RESUME" position, then releasing switch.

NOTE: When slide switch is moved to "OFF" position, pre-set speed of "RESUME" function is canceled from memory and must be reset when system is reactivated.

Higher speed can be set by pressing on accelerator pedal until new speed is reached and then pushing "SET/COAST" button. Lower speed can be obtained by lightly depressing brake pedal, allowing the vehicle to slow to desired speed and then depressing and releasing "SET/COAST" button.

CONTROL MODULE

Control module receives input voltage representing vehicle speed from speed sensor, which is driven by the speedometer cable. Control module has a low speed circuit that prevents operation at speeds below 30 MPH. See Fig. 1.

SERVO

Servo is controlled by control module and uses manifold vacuum to control throttle. Bead-link chain connects servo cable to throttle linkage. See Fig. 1.

CONTROL SWITCH

Control switch assembly is an integral part of turn signal switch lever. See Fig. 1.

RELEASE SYSTEM

Release system deactivates cruise control system when brake or clutch pedal is depressed. Either servo vent valve or mechanical vacuum vent switch admits atmospheric pressure into servo when brake pedal is depressed.

Fig. 1: Cruise Control System Components Courtesy of Chrysler Motors.

TROUBLE SHOOTING

NOTE: Vehicles with computerized engine controls, should be tested for stored computer codes. Codes and related problems must be repaired prior to cruise control diagnosis and repair. For additional information, see COMPUTERIZED ENGINE CONTROLS section.

SYSTEM WILL NOT ENGAGE

Restricted vacuum hose or no vacuum. Control switch or control module defective. Speed sensor defective. Clutch or brake light switch defective or misadjusted. Brake light switch wire disconnected. Open circuit between brake light switch and brake lights.

RESUME FEATURE INOPERATIVE

Defective servo ground connection. Defective control switch. ACCELERATE FUNCTION INOPERATIVE

Accelerate circuit in control module inoperative. Defective control switch.

SYSTEM RE-ENGAGES WHEN BRAKE PEDAL IS RELEASED

Defective control module. Mechanical vent valve not opening. Kink in mechanical vent valve hose. Brake light switch defective.

CARBURETOR THROTTLE DOES NOT RETURN TO IDLE POSITION

Improper linkage adjustment. ROAD SPEED CHANGES 2 MPH OR MORE WHEN SETTING SPEED

Centering adjustment wrong. Servo link misadjusted.

ENGINE ACCELERATES WHEN STARTED

Improper servo chain adjustment. Vacuum hose connections reversed at servo. Defective servo.

SYSTEM DISENGAGES ON LEVEL ROAD WITHOUT APPLYING BRAKES

Loose wire connection. Loose vacuum hose connection. Servo linkage broken. Defective brake light switch.

ERRATIC OPERATION

Reverse polarity of system wiring. Defective servo. Defective control module.

VEHICLE CONTINUES TO ACCELERATE WHEN "SET" BUTTON IS RELEASED

Servo or control module defective. SYSTEM ENGAGES BUT SLOWLY LOSES SET SPEED

Air leak at connections or in vacuum hoses. Air leak on vent valve on brake pedal.

ADJUSTMENTS

CONTROL MODULE ADJUSTMENT

NOTE: Control module adjustments are preset by manufacturer. If

other components in system appear to be functioning properly

and cruise control remains inoperative, perform following adjustments to determine if control module is functional.

1) Remove control module attaching screws or tie straps and
move control module downward for adjustment access. Turn centering
adjustment screw to 10 oclock position. Turn low speed adjustment
screw to 10 oclock position. Turn sensitivity adjustment screw fully
clockwise.

CAUTION: Adjustment potentiometers are extremely delicate. Carefully insert screwdriver and do not push or turn screws excessively hard. Maximum movement is 3/4 turn.

  • Adjustments are not precisely correct for vehicle, but are
    acceptable to determine if control module is functioning. Perform
    precise adjustments by road testing vehicle on level road. If
    adjustments have no effect on cruise control, replace control module.

  • If actual engagement speed is 2 MPH or more above selected
    speed, stop vehicle and turn centering screw 1/16 of a turn
    counterclockwise. Recheck engagement speed and adjust as necessary.

  • If engagement speed is 2 MPH or more below selected speed,
    turn centering screw 1/16 of a turn clockwise. Recheck engagement
    speed and adjust as necessary.

Fig. 2: Control Module Adjustment Screws Courtesy of Chrysler Motors.

VACUUM VENT VALVE

Depress brake or clutch pedal and hold in depressed position. Move vacuum vent valve toward bracket on pedal as far as possible. Release brake or clutch pedal.

TESTING

NOTE: Vehicles with computerized engine controls, should be tested for stored computer codes. Codes and related problems must be repaired prior to cruise control diagnosis and repair. For additional information, see COMPUTERIZED ENGINE CONTROLS section.

PRELIMINARY INSPECTION

Ensure cruise control wire harness is properly connected to

control module before starting diagnosis or repair procedure, as this connection is disturbed when Cruise Command System Tester (AM PC-1-R) is used. Poor connection at this point may be improperly diagnosed as control module malfunction.

Brake light and clutch switches should be properly adjusted. Ensure that all vacuum lines are correctly routed and tightly connected.

CRUISE COMMAND SYSTEM TESTS

Testing is performed with Cruise Command System Tester (AM PC-1-R). Remove wire harness connector from control module. Connect tester to wire harness connector. Perform tests as part of service diagnosis to determine cause and correction of system malfunction. Various tester lights are associated with specific components, circuits, etc.

CONTROL SWITCH CONTINUITY

Wrangler

NOTE: Voltage checks should show battery voltage. If resistance readings are incorrect, check circuit for an open or a short. Cruise control module terminal No. 1 grounds through connector at engine block.

Light No. 1 "OFF" (Set Switch)

With control switch in "ON" position, check for battery voltage between HAZ/STOP and in-line fuse, terminal No. 14 and ground terminal No. 1

Light No. 2 "OFF" (Control Switch & Speed Sensor) With control switch in "ON" position, check for battery voltage between HAZ/STOP and in-line fuse, terminal No. 5 and ground terminal No. 1. With ignition switch in "OFF" position, check resistance between terminals No. 2 and No. 3. Resistance should be 15-50 ohms.

Light No. 3 "OFF" (Brake Light Ground)

With ignition switch in "ON" position, install jumper wire between terminals No. 7 and No. 13. If brake lights do not turn on, check fuses and brake light switch connections.

Light No. 4 "OFF" (Throttle Position Feedback Sensor) With ignition switch in "ON" position, check for battery

voltage between gauge fuses at terminals No. 7 and No. 1.

With ignition switch in "OFF" position, check resistance

between terminals No. 2 and No. 11. Resistance should be 2400-4000

ohms. At idle resistance should be 2800-4300 ohms and at wide open

throttle resistance should be 4000 ohms.

Light No. 5 "OFF" (Resume/Accel/Vent Valve) With control switch in "RESUME/ACCEL" position, check for battery voltage between HAZ/STOP and in-line fuse, terminal No. 10 and ground terminal No. 1. With ignition switch in "OFF" position, check resistance between terminals No. 6 and No. 12. Resistance should be 30-50 ohms. Resistance between terminals No. 6 and ground, and terminal No. 12 and ground should be infinite (open).

Light No. 6 "OFF" (Resume/Accel/Charge Valve) With control switch in "RESUME/ACCEL" position, check for battery voltage between HAZ/STOP and in-line fuse, terminal No. 10 and ground terminal No. 1. With ignition switch in "OFF" position, check resistance between terminals No. 4 and No. 12. Resistance should be

30-50 ohms. Resistance between terminals No. 4 and ground, and terminal No. 12 and ground should be infinite (open).

WRANGLER CRUISE CONTROL TESTING

Conditions Lights "ON"

Control Switch "ON" & Set Switch Depressed No. 1

Control Switch "ON" No. 2

Ignition "ON" & Brake or Clutch Pedal Depressed No. 3 & No. 4

Cruise Control & Resume/Accel "ON" No. 5 & No. 6

Cruise & Resume/Accel "ON" & Engine Running (1) No. 5 & No. 6

(1) - Servo will pull throttle wide open. Keep RPM at a safe level by releasing cruise control switch.

Except Wrangler

Use 12-volt test light to test control switch continuity. Connect test light to wires as indicated in CONTROL SWITCH CONTINUITY TEST CHART. See Figs. 3 or 4.



SET/COAST (S/C) SW

POSITION SLIDER

1-2

1-3

1-4

2-3

2-4

3-4

Normal

Oft

0

Normal

On

Normal

R/A

Depressed

Off

Depressed

On

Depressed

R/A


Fig. 3: Cherokee, Comanche & Wagoneer Control Switch Continuity Test

Chart

Courtesy of Chrysler Motors.


- Closed - Open

Fig. 4: Grand Wagoneer Control Switch Continuity Test Chart Courtesy of Chrysler Motor.

CORRECT POWER SOURCE

Cherokee, Comanche & Wagoneer

  • With ignition switch and control switch "OFF", all test
    lights should be off. If any light is on, check Brown (7) wire is not
    connected directly to source of voltage.

  • Check for bad control switch. With ignition switch in
    "OFF" position, and control switch "ON". Light No. 2 should be on and
    lights No. 1, 3, 4, 5 and 6 should be off.

  • If light No. 2 is off, check speed sensor continuity,
    check speed sensor terminals to Gray and Drk. Blue wires, and check
    that terminals No. 2, 3, 5 and 7 (Gray, Drk. Blue and Lt. Green wires
    are not grounded).

Grand Wagoneer

With ignition and control switches in "OFF" position, test lights should be off. If one or more lights are on, remove Brown (5) wire at control module connector and check for direct source of voltage or repair defective control switch.

SYSTEM ELECTRICAL CONTINUITY

Cherokee, Comanche & Wagoneer

  • With ignition and control switches in "ON" position,
    lights No. 2, 3 and 4 should be on. Lights No. 1, 5 and 6 should be
    off. If light No. 2 is off, check speed sensor continuity, check speed
    sensor terminals to Gray and Drk. Blue wires, and check terminals No.
    2, 3, 5 and 7 (Gray, Drk. Blue and Lt. Green wires are not grounded).

  • If light No. 3 is off, check brake light switch and all
    Brown, Lt. Blue and Lt. Green wire connections. If light No. 4 is off,
    check terminals No. 2 and No. 11 at control module connector. Check
    continuity of throttle position feedback rheostat of servo.

Grand Wagoneer

  • With ignition and control switches in "ON" position,
    lights No. 1, 2, 3, and 4 should be on. Lights No. 5 and 6 should be
    off. If light No. 1 is off, check for blown fuse in brake light switch
    to control switch circuit. Check Red, Brown and Green wires at control
    switch for continuity to switch. Check Drk. Green wire (14) at control
    module connector for continuity to control module.

  • If light No. 2 is off, check speed sensor for correct
    output voltage. Check Gray and Drk. Blue wire at speed sensor
    connector for continuity to control module connector. Check terminals
    No. 2, 3, 5 and 7 at control module connector for proper connection to
    wires.

  • If light No. 3 is off, check brake and clutch switch
    adjustment. If light No. 4 is off, check for defective connection at
    terminals No. 2 and 11 on control module connector. Check operation of
    throttle position feedback rheostat on servo.

COAST CONTINUITY TEST

Cherokee, Comanche & Wagoneer

  • With ignition and control switches in "ON" position,
    depress and hold "SET/COAST" button. Lights No. 1, 2, 3 and 4 should
    be on. Lights No. 5 and 6 should be off. If light No. 1 is off, check
    voltage from brake light switch, check 4-amp in-line fuse of Pink
    wire, and check Pink, Brown and Drk. Green wires at control switch
    connector and Drk. Green (14) wire at control module connector for
    good connections.

  • If light No. 2 is off, check speed sensor continuity,
    check speed sensor terminals to Gray and Drk. Blue wires, and check
    terminals No. 2, 3, 5 and 7 (Gray, Drk. Blue and Lt. Green wires) for
    ground.

  • If light No. 3 is off, check brake light switch, check all
    Brown, Lt. Blue and Lt. Green wire connections. If light No. 4 is off,
    check terminals No. 2 and 11 at control module connector, and check
    continuity of throttle position feedback rheostat of servo.

SERVO CHARGE VALVE SOLENOID CONTINUITY

CAUTION: If engine is running, servo will move throttle to wide open position.

Grand Wagoneer

1) With ignition and control switches in "ON" position, depress and hold "SET/COAST" button. Lights No. 2, 3, 4, 5 and 6 should be on. Light No. 1 should be off. Light No. 4 will dim when

servo moves throttle to wide open position with engine operating.

  • If light No. 2 is off, check speed sensor for correct
    output voltage. Check Gray and Drk. Blue wire at speed sensor
    connector for continuity to control module connector. Check terminals
    No. 2, 3, 5 and 7 at control module connector for proper connection to
    wires.

  • If light No. 3 is off, check brake and clutch switch
    adjustment. If light No. 4 is off, check for defective connection at
    terminals No. 2 and 11 on control module connector. Check operation of
    throttle position feedback rheostat on servo.

  • If light No. 5 is off, check for defective connections at
    terminals No. 4 and 12 on control module connector. If necessary,
    replace defective servo. If light No. 6 is off, check for defective
    connection at terminals No. 6 and 12 on control module connector. If
    necessary, replace defective servo.

  • If all lights are off after depressing set/coast speed
    switch, check for blown fuse. Check for short circuits in Red, Pink
    and Brown wire circuits at control switch. If necessary, replace
    defective servo.

SYSTEM DISENGAGEMENT WITH BRAKE PEDAL DEPRESSED

Cherokee, Comanche & Wagoneer

  • With ignition and control switches in "ON" position and
    brake pedal depressed, lights No. 2 and 4 should be on. Lights No. 1,
    3, 5 and 6 should be off. Light No. 3 should be on when brake pedal is
    released.

  • If light No. 2 is off, check speed sensor continuity,
    check speed sensor terminals to Gray and Drk. Blue wires, and check
    terminals No. 2, 3, 5 and 7 (Gray, Drk. Blue and Lt. Green) for
    ground.

  • If light No. 4 is off, check terminals No. 2 and 11 at
    control module connector, and check continuity of throttle position
    feedback rheostat of servo.

Grand Wagoneer

  • With ignition and control switches in "ON" position and
    brake pedal depressed, lights No. 1, 2 and 4 should be on. Lights No.
    3, 5 and 6 should be off. Light No. 3 should be on when brake pedal is
    released.

  • If light No. 1 is off, check for blown fuse in brake light
    switch to control switch circuit. Check Red, Brown and Green wires at
    control switch connector for continuity to switch. Check Drk. Green
    wire (14) at control module connector for continuity to control
    module.

  • If light No. 2 is off, check speed sensor for correct
    output voltage. Check Gray and Drk. Blue wire at speed sensor
    connector for continuity to control module connector. Check terminals
    No. 2, 3, 5 and 7 at control module connector for proper connection to
    wires.

  • If light No. 4 is off, check for defective connection at
    terminals No. 2 and 11 on control module connector. Check operation of
    throttle position feedback rheostat on servo. If light No. 3 is off
    when brake pedal is released, check brake light switch adjustment.

"RESUME/ACCEL" FUNCTION

CAUTION: If engine is running, servo will move throttle to wide open position.

Cherokee, Comanche & Wagoneer

1) With ignition and control switches in "ON" position, slide and hold control switch in "R/A" position. Lights No. 2, 3, 4, 5 and 6

should be on. Light No. 1 should be off. Light No. 4 will dim when servo moves throttle to wide open position, if engine is running.

2) If light No. 2 is off, check speed sensor terminal

connections to control module through Gray and Drk. Blue wires. Check terminals No. 2, 3, 5 and 7 (Gray, Drk. Blue and Lt. Green wires) for ground.

  • If light No. 3 is off, check brake light switch, and check
    all Brown, Lt. Blue and Lt. Green wire connections. If light No. 4 is
    off, check terminals No. 2 and 11 at control module connector. Check
    continuity of throttle position feedback rheostat of servo.

  • If light No. 5 is off, check for bad connection at White
    (6) and Orange (12) wire terminals. If necessary, replace defective
    servo.

  • If all lights are off after moving control switch to "R/A"
    position, check for blown fuse or fuses, and check Red, Pink, Brown or
    White wires for shorts. If necessary replace defective servo.

Grand Wagoneer

  • With ignition and control switches in "ON" position, slide
    control switch to "R/A" position. All test lights should be on. Light
    No. 4 will dim when servo moves throttle to wide open position, if
    engine is running.

  • If light No. 1 is off, check for blown fuse in brake light
    switch to control switch circuit. Check Red, Brown and Green wires at
    control switch for continuity to switch.

  • If light No. 2 is off, check Gray and Drk. Blue wire at
    speed sensor connector for continuity to control module connector.

  • If light No. 3 is off, check brake light switch

adjustment. If light No. 4 is off, check for defective connection at terminals No. 2 and 11 on control module connector. Check operation of throttle position feedback rheostat on servo.

  • If light No. 5 is off, check for defective connections at
    terminals No. 4 and 12 on control module connector. If necessary,
    replace defective servo. If light No. 6 is off, check for defective
    connection at terminals No. 6 and 12 on control module connector. If
    necessary, replace defective servo.

  • If all lights are off after moving control switch to "R/A"
    position, check for blown fuse. Check for short circuits in Red, Pink
    and Brown wire circuits at control switch. If necessary, replace
    defective servo.

SPEED SENSOR TEST

  • Disconnect wire harness connector at speed sensor. Connect
    a voltmeter (set on low AC scale) to terminals from speed sensor.

  • Raise front and rear wheels of vehicle off ground and
    support vehicle with safety stands. Run engine (wheels spinning
    freely) at 30 MPH and note voltage.

  • Voltage should be approximately .9 volts. Increases of .1
    volts per each 10 MPH increase in speed should also be noticed. Turn
    off engine and stop wheels. Lower vehicle. Connect speed sensor wire
    harness.

SERVO TEST

  • With ignition switch in "OFF" position, disconnect servo
    wire harness connector. Remove vacuum hose from brake pedal vent valve
    nipple on servo. Disconnect servo cable from throttle linkage at
    carburetor.

  • Connect an ohmmeter between ground and Red. Ground and
    Orange. And Ground and White wire terminals of servo wire harness
    connector. See Fig. 5. Observe ohmmeter during each test. An infinite
    (open circuit) resistance should be indicated for each wire terminal.

3) If ohmmeter indicates less than infinite resistance on any
terminal, servo has short circuit to ground and must be replaced.
Short circuit will also cause damage to control module and it must be
replaced.

NOTE: Without sufficient load, solid state circuitry in control module will be damaged by excessive current flow.


Fig. 5: Servo Wire Harness Connector (Except Grand Wagoneer) Courtesy of Chrysler Motors.


  • If servo does not have any short circuits to ground,
    connect a vacuum gauge to brake pedal vent valve nipple. Connect a
    jumper wire from chassis ground to Orange wire terminal of servo wire
    harness connector.

  • Connect a second jumper wire to battery positive terminal
    and start engine. Momentarily connect jumper wire and simultaneously
    touch Red and White wire terminals in servo wire harness connector.

  • Vacuum should be indicated on gauge while jumper wire is
    in contact with wire terminals. Perform this test several times to
    make sure that solenoid valves are working properly.

  • With no voltage applied, solenoid charge valve is closed
    and solenoid vent valve is open. With 12 volts applied, solenoid
    charge valve is open and vent valve is closed.

  • Turn engine off and remove jumper wires. If servo is
    defective, replace it. If okay, connect vacuum hose, wire harness
    connector and throttle linkage to servo.