1988 JEEP CHEROKEE check engine

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 o'clock position. Turn low speed adjustment
screw to 10 o'clock 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.
2) 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.
3) 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.
4) 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

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
1) 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).
2) 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
1) 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.
2) 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.
3) 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
1) 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.
2) 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.
3) 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.
2) 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.
3) 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.
4) 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.
5) 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
1) 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.
2) 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.
3) 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
1) 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.
2) 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.
3) 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.
4) 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.
3) 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.
4) If light No. 5 is off, check for bad connection at White
(6) and Orange (12) wire terminals. If necessary, replace defective
servo.
5) 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
1) 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.
2) 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.
3) If light No. 2 is off, check Gray and Drk. Blue wire at
speed sensor connector for continuity to control module connector.
4) 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.
5) 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.
6) 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
1) Disconnect wire harness connector at speed sensor. Connect
a voltmeter (set on low AC scale) to terminals from speed sensor.
2) 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.
3) 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
1) 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.
2) 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.

\003
DO OR L O CKS - P O W ER

1988 J e ep C hero ke e
1988 Power Door Locks
JEEP
DESCRIPTION
Jeep vehicles with power door locks use a motor-actuated lock
system, controlled by rocker switches. Operation of switch assembly
controls the actuator motor.
Power door locks are protected by a 30-amp circuit breaker
located in the fuse block. Power door locks will not operate from
outside the vehicle.
TESTING
SWITCH
Using ohmmeter, test switches for continuity. Connect
ohmmeter across terminals as shown. See Fig. 1. Continuity should
exist between terminals in all positions.
Fig. 1: Checking Switch Continuity
Courtesy of Chrysler Motors.
ACTUATOR MOTOR
Connect ammeter to actuator motor terminals. Operate door
switch and note reading. Current draw should not exceed 8 amps at room
temperature. Actuator should complete full travel within one second.
Replace actuator motor if not within specification.
CIRCUIT BREAKER
1) Disconnect harness connector from fuse block. Using test
light, check fuse block harness connection for voltage. If there is no
battery voltage at connection, check for burnt fusible link in engine
compartment.
2) Check circuit breaker continuity if voltage exists. Using
ohmmeter, test circuit breaker for continuity. Replace circuit breaker
if no continuity exists.
3) If circuit breaker tests okay, check for battery voltage
at circuit breaker connection of fuse block with wiring harness
installed. If voltage exists at wiring harness but not at circuit
breaker connection, check fuse block for damage.
REMOVAL & INSTALLATION

DRIV E B ELT R O UTIN G

1988 J e ep C hero ke e
1983-88 ENGINE COOLING
Jeep Drive Belt Routing
Cherokee, Comanche, Wagoneer, Wrangler, Grand Wagoneer
DESCRIPTION
Two drive belt systems are used on Jeep vehicles. The
conventional V-Belt and the single Serpentine or V-Ribbed belt.
The single (Serpentine or V-Ribbed) drive belt system
has been adopted by several manufacturers as a replacement for
multiple V-Belt systems previously offered. The Serpentine belt
requires a suitable belt tensioner similar to those used to control
timing belt tension.
Use of a tensioner allows engine accessories to be mounted
rigidly on the engine. The single belt drive system has a predicted
life of 100,000 miles before replacement is required.
The belt tensioner has a wide functional range and is
capable of maintaining tension during the expected life of the belt.
Tensioner cannot compensate for extreme belt lengths. Poor tension
control and possible tensioner damage can result from excessive belt
length.
INSPECTION
Inspect belt for fraying. If fraying has occurred, ensure
belt and tensioner are aligned properly. See Fig. 1. If tensioner has
reached its limit of travel, belt is excessively stretched and
replacement of belt is required. If excessive noise is noticed from
tensioner or idler, check for possible bearing failure. Small cracks
in the back of the belt are acceptable. Do not apply "Belt Dressing"
or any other additive to serpentine belt.
Fig. 1: Serpentine Belt Alignment
Courtesy of Ford Motor Co.
DRIVE BELT ROUTING

Vibration can come from many sources. Before overhauling
driveline, check other sources of possible vibration as follows:
* Tires and wheels - Check tire inflation and wheel balance.
Check for foreign objects in tread, damaged tread, mismatched
tread patterns or incorrect tire size.
* Center Bearing - Tighten drive shaft center bearing
mounting bolts. If bearing insulator is deteriorated or
oil-soaked, replace it.
* Engine & Transmission Mountings - Tighten mounting bolts.
If mountings are deteriorated, replace them.
* Drive Shaft - Check drive shaft for damage or dents that
could affect balance. Check for undercoating adhering to
shafts. If present, clean shafts thoroughly.
* Universal Joints - Check for foreign material stuck in
joints. Check for loose bolts and worn bearings.
ADJUSTMENTS
DRIVE SHAFT PHASING
One-Piece Shafts
Check that flanges on either end of drive shaft are in same
plane. Often there are arrows on slip joint and drive shaft to aid in
alignment. See Fig. 2. If flanges are not in same plane, disassemble
universal joint and align.
Fig. 2: Slip Joint Alignment Arrows
Align arrows for proper shaft phasing.
2-Piece Shafts
1) All General Motors models with 32 splines use keys on
spline and slip joint, which can only mate in correct position. On
most models with 2-piece shafts, proper phasing is accomplished by
keys on spline and slip joint.