Jeep Liberty KJ. Manual — part 643
Possible Causes
(A209) PCM FUSED B+ CIRCUIT
PCM NO RESPONSE
(F1) (F26) PCM FUSED IGNITION SWITCH OUTPUT CIRCUITS
(Z130) (Z131) PCM GROUND CIRCUITS
CRANKSHAFT POSITION SENSOR
(F855) 5-VOLT SENSOR OPEN/SHORTED
(F855) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
(F856) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
PCM
Diagnostic Test
1.
(A209) PCM FUSED B+ CIRCUIT
NOTE: The scan tool and cable must be operating properly for the
results of this test to be valid.
NOTE: Make sure the ignition switch was on while trying to com-
municate with the PCM.
Turn the ignition off.
Disconnect the C1 PCM harness connector.
CAUTION: Do not probe the PCM harness connectors. Probing the
PCM harness connectors will damage the PCM terminals resulting
in poor terminal to pin connection. Install Miller Special Tool #8815
to perform diagnosis.
Using a 12-volt test light connected to ground, probe the appropriate
terminal of special tool #8815.
Does the test light illuminate brightly?
Yes
>> Go To 2
No
>> Repair the open or short to ground in the (A209) Fused B+
circuit. Inspect and replace fuses as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
2.
(F1) (F26) PCM FUSED IGNITION SWITCH CIRCUITS
Using a 12-volt test light connected to ground, probe the PCM Fused
Ignition Switch Output circuit in the appropriate terminals of special tool
#8815.
Does the test light illuminate brightly?
Yes
>> Go To 3
No
>> Repair the (F1) and (F26) Ignition Switch Output circuits.
Inspect and replace fuses as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
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ENGINE ELECTRICAL DIAGNOSTICS
KJ
3.
(Z130) (Z131) PCM GROUND CIRCUITS
Using a 12-volt test light connected to battery voltage, probe the (Z130)
and (Z131) PCM ground circuits in the appropriate terminals of special
tool #8815.
Does the test light illuminate brightly?
Yes
>> Go To 4
No
>> Repair the PCM ground circuits.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
4.
(F855) 5-VOLT SUPPLY CIRCUIT
Turn the ignition off.
Connect the C1 PCM harness connector.
Disconnect the Crankshaft Position Sensor harness connector.
Ignition on, engine not running.
Measure the voltage on the (F855) 5-volt Supply circuit.
Is the voltage between 4.5 and 5.2 volts?
Yes
>> Go To 5
No
>> Go To 6
5.
CKP SENSOR
Turn the ignition off.
Disconnect the TP Sensor harness connector.
Ignition on, engine not running.
Measure the voltage on the (F855) 5-volt Supply circuit in the TP Sen-
sor harness connector.
Is the voltage between 4.5 and 5.2 volts?
Yes
>> If communication is available with a PCM on a like vehicle,
replace and program the Powertrain Control Module per
Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No
>> Replace the Crankshaft Position Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
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ENGINE ELECTRICAL DIAGNOSTICS
9 - 631
6.
(F855) 5-VOLT SENSOR OPEN/SHORTED
Turn the ignition off.
Disconnect the TP Sensor/Throttle Body harness connector.
Ignition on, engine not running.
Measure the voltage on the (F855) 5-volt Supply circuit.
Disconnect all the sensors that use the (F855) 5-volt Supply circuit.
Did the voltage return to 4.5 to 5.2 volts when disconnecting
any of the sensors.
Yes
>> Replace the sensor that is pulling down the (F855) 5-volt
supply.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No
>> Go To 7
7.
(F855) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
Turn the ignition off.
Disconnect C2 PCM harness connector.
Disconnect all the sensors that share the (F855) 5-volt Supply circuit.
Measure the resistance between ground and the (F855) 5-volt Supply
circuit at one of the sensor harness connectors.
Is the resistance below 100 ohms?
Yes
>> Repair the short to ground in the (F855) 5-volt Supply cir-
cuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No
>> Go To 8
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ENGINE ELECTRICAL DIAGNOSTICS
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8.
(F856) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
Disconnect all the sensors that share the (F856) 5-volt Supply circuit.
Measure the resistance between ground and the (F856) 5-volt Supply
circuit at one of the sensor harness connectors.
Is the resistance below 100 ohms?
Yes
>> Repair the short to ground in the (F856) 5-volt Supply cir-
cuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No
>> Go To 9
9.
PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal
push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and
Ground circuits.
Were there any problems found?
Yes
>> Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
>> Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
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ENGINE ELECTRICAL DIAGNOSTICS
9 - 633
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