Diagnostic Procedure

WARNING: This page is about a different car, the 2005 Jeep Liberty. However, it is still accessible from the selected car via links, so may be relevant.

DIAGNOSTIC PROCEDURES - CAN C BUS PERFORMANCE [FCM] (DIESEL ONLY)

TEST	ACTION	APPLICABILITY
1	Turn the ignition off and wait 1 minute. Disconnect the FCM harness connector. Disconnect the ECM harness connectors. Disconnect the ABS harness connector. Measure the resistance of both the CAN C Bus (+) circuit and the CAN C Bus (-) circuit between the FCM harness connector and both the ECM harness connector and the ABS harness connector. Is the resistance above 5.0 ohms on either Bus circuit? Yes --> Repair the CAN C Bus (+) and/or CAN C Bus (-) circuit for an open. Perform BODY VERIFICATION TEST - VER 1 . No --> Go To 2	All
2	Turn the ignition off and wait 1 minute. Gain access to the FCM harness connector. NOTE: Ensure the ABS, FCM and ECM harness connectors are connected. While backprobing, measure the resistance between ground and both the CAN C Bus (+) circuit and the CAN C Bus (-) circuit. Is the resistance below 5.0 ohms on either Bus circuit? Yes --> Disconnect each module one at a time. Replace module that when disconnected the short to ground condition was eliminated. If the short to ground condition is still present with all the CAN modules disconnected, repair the circuit for a short to ground. Perform BODY VERIFICATION TEST - VER 1 . No --> Go To 3	All
3	Turn the ignition off and wait 1 minute. Gain access to the FCM harness connector. NOTE: Ensure the ABS, FCM and ECM harness connectors are connected. Turn the ignition on. While backprobing, measure the voltage between ground and both the CAN C Bus (+) circuit and the CAN C Bus (-) circuit. Is the voltage above 5.0 volts on either Bus circuit? Yes --> Disconnect each module one at a time. Replace module that when disconnected the short to voltage condition was eliminated. If the short to voltage condition is still present with all the CAN modules disconnected, repair the ckt for a short to voltage. Perform BODY VERIFICATION TEST - VER 1 . No --> Go To 4	All
4	Turn the ignition off and wait 1 minute. Disconnect the ABS harness connector. Disconnect the ECM harness connectors. Disconnect the FCM harness connector. Measure the resistance between the CAN C Bus (+) circuit and the CAN C Bus (-) circuit. Is the resistance below 5.0 ohms? Yes --> Repair the short between the CAN C Bus (+) circuit and the CAN C Bus (-) circuit. Perform BODY VERIFICATION TEST - VER 1 . No --> Go To 5	All
5	Turn the ignition off and wait 1 minute. Disconnect the FCM harness connector. Disconnect the ECM harness connectors. Disconnect the ABS harness connector. Measure the resistance of both the CAN C Bus (+) circuit and the CAN C Bus (-) circuit to all other circuits in each of the CAN C bus modules (ECM, ABS and FCM) Is the resistance below 5.0 ohms between any other circuit? Yes --> Repair the CAN C Bus (+) and/or CAN C Bus (-) circuit for a short to other circuits. Perform BODY VERIFICATION TEST - VER 1 . No --> Go To 6	All
6	Turn the ignition off and wait 1 minute. Disconnect the ABS harness connector. NOTE: Make sure both the ECM and the FCM harness connectors are connected before taking this measurement. Measure the resistance between the CAN C Bus (+) circuit and the CAN C Bus (-) circuit in the ABS harness connector. Is the resistance 60.0 ohms, +/- 3.0 ohms? Yes --> Replace the ABS Control Module in accordance with the service information. Perform BODY VERIFICATION TEST - VER 1 . No --> Go To 7	All
7	Turn the ignition off and wait 1 minute. Disconnect the FCM harness connector. NOTE: Make sure the ECM harness connectors are connected before taking this measurement. Measure the resistance between the CAN C Bus (+) circuit and the CAN C Bus (-) circuit in the FCM harness connector. Is the resistance 120 ohms, +/- 2.0 ohms? Yes --> Replace the Front Control Module in accordance with the service information. Perform BODY VERIFICATION TEST - VER 1 . No --> Replace the Engine Control Module in accordance with the service information. Perform BODY VERIFICATION TEST - VER 1 .	All