1988 JEEP CHEROKEE jump start

connect Fuel Pressure Gauge (J-34730-1). See Fig. 3. Start engine and
observe fuel pressure. With vacuum hose connected to pressure
regulator, pressure should be about 31 psi (2.2 kg/cm
)), and about 39
psi (2.7 kg/cm)) with vacuum hose disconnected.
2) If pressure is not as specified, inspect fuel supply and
return lines for kinks and obstructions. If fuel lines are okay,
replace pressure regulator. Remove gauge and install cap on test port.
Fuel Flow
1) Remove cap from the pressure test port on the fuel rail.
See Fig. 3 . Connect piece of hose to port and place other end in
graduated container of at least one quart (1L) capacity.
2) Pinch off fuel return line. Run fuel pump by placing
jumper wire between terminals "D1-5" and "D1-6" of diagnostic
connector "D1". If fuel flow is less than one quart (1L) in one
minute, replace fuel pump. Remove hose and install test port plug.
Fig. 3: Location of Fuel Pressure Test Port
Fuel Injector Test
See the FUEL INJECTOR DIAGNOSTICS chart near the end of this
article. See Fig. 9

Resistance value should be about 22 ohms. Measure resistance between
either terminal and battery negative post. Resistance value should be
infinite. If resistance values are not as specified, replace relay. If
okay, reconnect electrical connectors.
2) Disconnect electrical connector from "SOL" terminal.
Connect voltmeter between terminal and battery negative post. While
observing voltmeter, turn ignition switch to "START" position. If 12
volts is not indicated, check and repair wiring harness, bulkhead
connector, and/or ignition switch. If battery voltage is present, go
to next step.
3) If battery voltage is present, but starter relay does not
work, place transmission in Park (Neutral for man. trans.) and apply
parking brake. Disconnect electrical connector from terminal "I" (Dark
Green wire) and apply battery voltage to terminal. Using a jumper
wire, touch terminal "G" to ground. If relay does not click, replace
relay. If relay does click, repair ground circuit.
Fig. 7: Design & Function of Relays
REMOVAL & INSTALLATION

2) Connect the DRB-II to the transmission diagnostic
connector. See RETRIEVING FAULT CODES under SELF-DIAGNOSTIC SYSTEM for
diagnostic connector location.
CAUTION: If the vehicle is in 3rd or OD position and feels like it
is stuck in 3rd or jumping from 2-1 or 3-1, perform
TEST 10A - TESTING FOR INTERMITTENT SPEED SENSOR test below.
3) With the DRB-II, perform SYSTEM TEST. See SYSTEM TEST MODE
under DRB-II OPERATING MODES .
4) The DRB-II will instruct you to do some actions during the
System Test. The DRB-II will then look for the action to happen and
automatically go to the next test function. If you perform the
required action and the DRB-II does not move to the next function,
press ENTER. The DRB-II will continue the testing.
5) When the DRB-II states "VEHICLE DRIVE", the vehicle be
must be driven at a speed above 4 miles per hour to ensure accurate
testing of the vehicle speed sensor. Afterwards, the DRB-II will
display any fault codes that may be present.
6) When the system test is complete, if there are any fault
codes present, the DRB-II will automatically display the code(s).
7) There are two types of faults for the transmission
solenoids. They are displayed as "FAULT STORED" and "FAULT PRESENT".
Note that the tests are different in the chart below.
8) Perform the tests shown below in response to the indicated
fault codes.
NOTE: ALWAYS start diagnosis with the most recent code.
CODE-TO-TEST MENU
CODE-TO-TEST MENU







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Code:  Solenoid Affected:  Fault Status:  Perform: 








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None  None Affected  No Faults  Test 2A 








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700  Solenoid No. 1  Fault Present  Test 4A 








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700  Solenoid No. 1  Fault Stored  Test 3A 








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700  Solenoid No. 2  Fault Present  Test 4B 








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700  Solenoid No. 2  Fault Stored  Test 3A 








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700  Solenoid No. 3  Fault Present  Test 4C 








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700  Solenoid No. 3  Fault Stored  Test 3A 








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702  Speed Sensor Fault   Test 5A 








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703  Gear Select Fault   Test 6A 








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705  TPS Fault   Test 7A 








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708  Wrong TCU   Test 9A 











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TEST 2A - VERIFICATION TEST
NOTE: Perform TEST 1A - VERIFICATION OF THE COMPLAINT
before proceeding.

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

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.
4) 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.
5) 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.
6) 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.
7) 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.
8) 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.
Fig. 5: Servo Wire Harness Connector (Except Grand Wagoneer)
Courtesy of Chrysler Motors.

EN G IN E C O OLIN G F A N

1988 J e ep C hero ke e
1987-88 ENGINE COOLING
Thermostatically Controlled Electric Fans
Cherokee, Comanche, Wagoneer
DESCRIPTION & OPERATION
On Cherokee, Comanche and Wagoneer models with a 4.0L engine,
A/C and/or heavy duty cooling system, an auxiliary electric fan is
used. The auxiliary fan is controlled by a relay mounted on the left
inner fender panel. A radiator temperature switch attached to the
radiator outlet tank above the lower radiator hose senses engine
coolant temperature.
When coolant temperature is more than 190(0)F (88(0)C), t\
he
radiator coolant temperature switch closes allowing current from the
ignition switch to flow through the fan relay to ground activating the
relay. When relay is activated, battery voltage is supplied to the fan
causing it to operate. When coolant temperature is below 190(0)F
(88(0)C), the radiator coolant temperature switch opens preventing t\
he
relay from being grounded and electric cooling fan from being
energized.
When the A/C (if equipped) is turned on, the Electronic
Control Unit (ECU) grounds the A/C relay coil allowing current to flow\
through it. This activates the A/C relay which then supplies current
to the A/C clutch, fan diode assembly and cooling fan relay. The
cooling fan relay is activated and the fan operates. Whenever the A/C
is used, regardless of engine coolant temperature, the auxiliary
electric cooling fan operates.
TESTING
NOTE: For following tests, refer to fan relay connector terminal
identification and fan controls identification. See Figs. 1
and 2.
With Air Conditioning
1) If electric cooling fan does not work all the time, go to
step 3). If electric cooling fan is inoperative when A/C compressor
operates, start engine and turn A/C on. Disconnect fan relay
connector. Fan relay is located on left inner fender panel.
2) Using a voltmeter, check for voltage at fan relay
connector terminal No. 2. If voltmeter does not read battery voltage,
replace fan diode assembly.
3) Disconnect fan relay connector. Fan relay is located on
left inner fender panel. Using a jumper wire with an in-line 25-amp
fuse, supply battery voltage to fan relay connector terminal No. 4.
4) If fan operates, motor is okay. Go to next step. If fan
motor does not operate, check continuity between fan relay connector
terminal No. 4 and body ground connections. If continuity exists,
replace fan motor. If continuity does not exist, repair open and
retest.
5) Disconnect fan relay connector. Turn ignition switch to
the "RUN" position. Check continuity between fan relay connector
terminal No. 5 and body ground connections. If continuity does not
exist, repair open circuit. If continuity exists, go to next step.
6) Using a jumper wire with an in-line 25-amp fuse, jump
across fan relay connector terminals No. 1 and No. 4. If fan motor
operates, go to next step. If fan motor does not operate, repair fan

other end of hose into a container of at least one liter or more
capacity.
5) Run fuel pump by installing a jumper wire into diagnostic
connector terminals D1-5 and D1-6. Be sure to pinch off fuel return
line or most of fuel will be returned to fuel tank.
EGR Solenoid Test
1) Verify that vacuum is present at vacuum fitting "C" of
EGR solenoid. See Fig. 4. Remove vacuum connector from "A" and "B".
Connect a vacuum gauge to "B".
2) Start and idle engine. There should be no vacuum at "B".
Disconnect electrical connector "D" from solenoid. There should now
be vacuum at "B".
Fig. 4: EGR Solenoid Test Points
Courtesy of Chrysler Motors.
MAP Sensor Test
1) Inspect MAP sensor hoses and connections. Repair as
necessary. With ignition on and engine off, test MAP sensor output
voltage at connector terminal "B". (Marked on sensor body). See
Fig. 5 . Output voltage should be 4 to 5 volts.
2) To verify wiring harness condition, test ECU terminal C-6
for same voltage described. Test MAP sensor supply voltage at sensor
connector terminal "C" with ignition on.

3) Using ohmmeter, check MAP sensor ground circuit between
terminals No. 17 and 2 of ECU connector. If circuit is incomplete,
check sensor ground connection on bellhousing, near starter motor.
Replace ECU if ground is good. If terminal No. 17 is shorted to 12
volts, repair problem BEFORE ECU is replaced.
DIAGNOSTIC TOOLS
To properly test throttle body fuel injection system,
service technician must have the following equipment available:
* Digital volt-ohmmeter (DVOM) or volt-ohmmeter with minimum input
impedance of one megohm.
* 12-volt test light, jumper wires and probes.
* Hand vacuum pump with gauge.
* Ignition timing light.
Fig. 4: Jeep/Renix Fuel Injection Diagnostic Connectors
Courtesy of Chrysler Motors.
DIAGNOSTIC TESTS