Jeep Liberty KJ. Manual — part 648
Theory of Operation
The Accelerator Pedal Position Sensor (APP) is a device that contains 2 separate potentiometer type sensors. Each
sensor has its own 5-volt supply circuit, sensor ground circuit and signal circuit.
The APP Sensor 2 signal should always be approximately 1/2 the voltage of the APP Sensor 1 signal.
Possible Causes
APP SENSOR OPERATION
APP SENSOR CIRCUIT 1 HIGH RESISTANCE
APP SENSOR CIRCUIT 2 HIGH RESISTANCE
Diagnostic Test
1.
APP SENSOR IDLE VOLTAGE
Inspect the Accelerator Pedal Position Sensor for proper travel from the
rest position to the fully depressed position.
Turn the ignition on.
With the accelerator pedal in the rest position, use a voltmeter to back-
probe the (K23) Accelerator Pedal Position Sensor 1 and the (K29)
Accelerator Pedal Position Sensor 2 Signal circuits at the Accelerator
Pedal Position Sensor harness connector with the accelerator pedal in
the at rest position.
Is the voltage between 0.42 and 0.51 volt for sensor 1 and 0.19
and 0.28 volt for sensor 2?
Yes
>> Go To 2
No
>> Check the wiring and connectors related to the Accelerator
Pedal Position Sensor. If OK, replace the Accelerator Pedal
Position Sensor.
Perform the ECM Verification Test Ver. 1 (Refer to 9 -
ENGINE - DIAGNOSIS AND TESTING).
2.
APP SENSOR
While back probing, measure the voltage of the (K23) Accelerator Pedal
Position Sensor Signal 1 and (K29) Accelerator Pedal Position Sensor
Signal 2 circuits at the ECM.
Monitor the voltmeter while slowly pressing the accelerator pedal com-
pletely down.
Did the voltage for both sensors increase smoothly with pedal
travel?
Yes
>> Go To 3
No
>> Replace the Accelerator Pedal Position Sensor in accor-
dance with the Service Information.
Perform the ECM Verification Test Ver. 1 (Refer to 9 -
ENGINE - DIAGNOSIS AND TESTING).
9 - 650
ENGINE DIESEL DIAG
KJ
3.
APP SENSOR WIDE OPEN THROTTLE VOLTAGE
Using a voltmeter backprobe the Accelerator Pedal Position Sensor har-
ness connector and read the voltage for (K23) Accelerator Pedal Posi-
tion Sensor 1 and (K29) Accelerator Pedal Position Sensor 2 Signal
circuits.
Fully depress the accelerator pedal.
Is the voltage between 4.45 and 4.75 volts for #1 and 2.15 and
2.45 volts for #2?
Yes
>> Test Complete.
No
>> Check the wiring and connectors related to the APP Sensor.
If OK, replace the Accelerator Pedal Position Sensor.
Perform the ECM Verification Test Ver. 1 (Refer to 9 -
ENGINE - DIAGNOSIS AND TESTING).
KJ
ENGINE DIESEL DIAG
9 - 651
*CHECKING THE ECM POWER AND GROUND CIRCUITS
For a complete wiring diagram Refer to Section 8W
9 - 652
ENGINE DIESEL DIAG
KJ
Possible Causes
(K342) ASD RELAY CONTROL CIRCUIT OPEN
(K347) ASD RELAY OUTPUT CIRCUIT(S) OPEN
(Z131) ECM GROUND CIRCUIT(S) OPEN
FUSED ASD RELAY BATTERY SUPPLY CIRCUIT OPEN
(F26)
FUSED IGNITION SWITCH (START) OUTPUT CIRCUIT OPEN
(F1) FUSED IGNITION SWITCH (START/RUN) OUTPUT CIRCUIT OPEN
SUBSTITUTE ASD RELAY
(K342) ASD RELAY CONTROL CIRCUIT SHORTED TO VOLTAGE
Diagnostic Test
1.
ECM GROUND CIRCUIT(S) OPEN
Turn the ignition off.
Disconnect the ECM harness connectors.
Using a 12-volt test light connected to 12-volts, check each of the ECM
ground circuits in ECM harness connector C2 cavities 2, 4 and 6.
Did the test light illuminate for each cavity?
Yes
>> Go To 2
No
>> Repair the ECM Ground circuit(s) for an open.
Perform the ECM Verification Test Ver. 1 (Refer to 9 -
ENGINE - DIAGNOSIS AND TESTING).
2.
FUSED IGNITION SWITCH START OUTPUT CIRCUIT OPEN
Turn the ignition to the Start position.
Using a 12-volt test light connected to ground, check the Fused Ignition
Switch (Start) Output circuit in ECM harness connector C2 cavity 22.
Is the test light on?
Yes
>> Go To 3
No
>> Repair the Fused Ignition Switch (Start) Output circuit for an
open.
Perform the ECM Verification Test Ver. 1 (Refer to 9 -
ENGINE - DIAGNOSIS AND TESTING).
KJ
ENGINE DIESEL DIAG
9 - 653
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