Jeep Liberty KJ. Manual — part 736
3.
CHECK FOR RELATED TCM DTCS
NOTE: The TCM Receives vehicle speed messages via CAB Bus from the ABS module. An interruption on
the CAN Bus can cause this fault to set.
Turn the ignition on.
With the scan tool, check the TCM for DTCs.
Are any ABS CAN Bus Message or Vehicle Speed related TCM DTCs present?
Yes
>> Replace the CAB in accordance with the Service Information.
Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
No
>> Replace and program the Engine Control Module in accordance with the Service Information.
Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
9 - 1002
ENGINE DIESEL DIAG
KJ
P0504-BRAKE SWITCH SIGNAL CIRCUITS PLAUSIBILITY WITH REDUNDANT
CONTACT
KJ
ENGINE DIESEL DIAG
9 - 1003
For a complete wiring diagram Refer to Section 8W
•
When Monitored:
With the ignition on.
•
Set Condition:
The Primary Brake Switch Signal and Secondary Brake Switch Signal inputs to the ECM do not agree.
Possible Causes
INTERMITTENT CONDITION
BRAKE LAMP SWITCH - SENSE CKT OPEN
BRAKE LAMP SWITCH FUSED B+ CIRCUIT OPEN
BRAKE SWITCH SENSE CIRCUIT SHORTED TO GROUND
BRAKE LAMP SWITCH - OUTPUT OPEN
BRAKE SWITCH SENSE CIRCUIT OPEN
BRAKE SWITCH SENSE GROUND CIRCUIT OPEN
BRAKE LAMP SWITCH OUTPUT CIRCUIT SHORTED TO VOLTAGE
BRAKE LAMP SWITCH OUTPUT CIRCUIT OPEN
ENGINE CONTROL MODULE - BRAKE SWITCH SENSE
ENGINE CONTROL MODULE - INTERNAL
ENGINE CONTROL MODULE - PRIMARY BRAKE SIGNAL
Diagnostic Test
1.
CHECK THE PRIMARY BRAKE SWITCH STATUS WITH THE SCAN TOOL
NOTE: If the ECM detects and stores a DTC, the ECM also stores the engine/vehicle operating conditions
under which the DTC was set. Some of these conditions are displayed on the scan tool at the same time the
DTC is displayed.
NOTE: Before erasing stored DTCs, record these conditions. Attempting to duplicate these conditions may
assist when checking for an active DTC.
Turn the ignition on.
While observing the PRIMARY BRAKE SWITCH status on the scan tool display, press and release the brake pedal
several times.
Does the scan tool display PRIMARY BRAKE SWITCH: PRESSED and RELEASED for the appropriate
pedal position?
Yes
>> Go To 2
No
>> Go To 10
2.
CHECK THE SECONDARY BRAKE SWITCH STATUS WITH THE SCAN TOOL
Turn the ignition on.
While observing the SECONDARY BRAKE SWITCH status on the scan tool display, press and release the brake
pedal several times.
Does the scan tool display SECONDARY BRAKE SWITCH: PRESSED and RELEASED for the appropri-
ate pedal position
Yes
>> Refer to the *CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING)
No
>> Go To 3
9 - 1004
ENGINE DIESEL DIAG
KJ
3.
BRAKE SWITCH SENSE CIRCUIT VOLTAGE
Turn the ignition off.
Disconnect the Brake Lamp Switch harness connector.
Turn the ignition on.
Measure the voltage between the Brake Switch Sense circuit and
ground.
Is the voltage above 9.0 volts?
Yes
>> Go To 4
No
>> Go To 7
4.
BRAKE LAMP SWITCH - SENSE CKT OPEN
Disconnect the Brake Lamp Switch harness connector.
Turn the ignition on.
While monitoring the SECONDARY BRAKE SWITCH status with the scan tool, connect a jumper wire between
ground and the Secondary Brake Switch Sense circuit.
Does the scan tool display change from PRESSED to RELEASED?
Yes
>> Adjust or replace the Brake Lamp Switch in accordance with the Service Information.
Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
No
>> Go To 5
5.
BRAKE SWITCH SENSE GROUND CIRCUIT OPEN
Turn the ignition off.
Disconnect the Brake Lamp Switch harness connector.
Measure the resistance between ground and the Secondary Brake
Switch Ground circuit.
Is the resistance below 10.0 ohms?
Yes
>> Go To 6
No
>> Repair the Brake Switch Sense Ground circuit for an open.
Perform the ECM Verification Test Ver. 1 (Refer to 9 -
ENGINE - DIAGNOSIS AND TESTING).
KJ
ENGINE DIESEL DIAG
9 - 1005
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