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Front Control Module (FCM)






U0019-CAN B BUS





For a complete wiring diagram, refer to the Wiring Information Electrical Diagrams.

- When Monitored:
With the ignition on.

- Set Condition:
The Front Control Module (FCM) detects an open, a short high, a short low or a short together in either of the CAN B Bus circuits.





1. TEST FOR INTERMITTENT CONDITION
1. Turn the ignition on.
2. Using the scan tool, record and erase FCM DTCs.
3. Cycle the ignition from on to off three times.
4. Turn the ignition on.
5. Using the scan tool, read active FCM DTCs.

Does the scan tool display this DTC as active?

Yes

- Go To 2

No

- The conditions that caused this code to set are not present at this time. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors.

2. MEASURE VOLTAGE AT FCM
1. Gain access to the FCM C1 harness connector, but do not disconnect.
2. Backprobe and measure the voltage on both the (D55) CAN B Bus (+) and the (D54) CAN B (-) circuits.

Does the voltage read approximately 4.65 - 4.98 volts on the (D54) CAN B Bus (-) and 0.39 - 0.46 volts on the (D55) CAN B (+) circuits?

Yes

- Go To 3

No - Voltage Between 0.3 - 0.7 of a volt on both circuits

- Go To 9

No - Voltage Reads 0 Volts on either circuit

- Go To 7

No - Voltage Above 10 Volts on either circuit

- Go To 5

3. (D55) CAN B BUS (+) CIRCUIT OPEN




1. Turn the ignition on.
2. With the scan tool select ECU View.
3. Using a fused jumper wire, connect one end to ground and with the other end backprobe the (D54) CAN B Bus (-) circuit at the FCM C1 harness connector.

NOTE: A red "X" will appear next to modules that can no longer communicate on the Bus.

Did a red "X" appear next to any modules on the scan tool?

Yes

- Using the Wiring Diagrams to further isolate the open in the circuit, repair the (D55) CAN B Bus (+) circuit for an open.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Go To 4

4. (D54) CAN B BUS (-) CIRCUIT OPEN




1. With the scan tool select ECU View.
2. Using a fused jumper wire, connect one end to ground and with the other end backprobe the (D55) CAN B Bus (+) circuit at the FCM C1 harness connector.

NOTE: A red "X" will appear next to modules that can no longer communicate on the Bus.

Did a red "X" appear next to any modules on the scan tool?

Yes

- Using the Wiring Diagrams to further isolate the open in the circuit, repair the (D54) CAN B Bus (-) circuit for an open.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Inspect the wiring and connectors for damage. If ok, replace and program the Front Control Module.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

5. (D55) CAN B BUS (+) CIRCUIT FOR A SHORT TO VOLTAGE




1. Turn the ignition off.
2. Disconnect the Front Control Module C1 harness connector.
3. Turn the ignition on.
4. Measure the voltage between the (D55) CAN B Bus (+) circuit and ground.

Is the voltage above 10.0 volts?

Yes

- Disconnect each CAN B Bus module one at a time while observing the voltage to determine if the short is caused by an internal short within a module. Replace the module,, that when disconnected eliminates the short to voltage. If the short condition is still present with all CAN B Bus modules disconnected use the Wiring Diagrams to help isolate and repair the (D55) CAN B Bus (+) circuit for a short to voltage.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Go To 6

6. (D54) CAN B BUS (-) CIRCUIT FOR A SHORT TO VOLTAGE




1. Measure the voltage between the (D54) CAN B Bus (-) circuit and ground.

Is the voltage above 10.0 volts?

Yes

- Disconnect each CAN B Bus module one at a time while observing the voltage to determine if the short is caused by an internal short within a module. Replace the module,, that when disconnected eliminates the short to voltage. If the short condition is still present with all CAN B Bus modules disconnected use the Wiring Diagrams to help isolate and repair the (D54) CAN B Bus (-) circuit for a short to voltage.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Inspect the wiring and connectors for damage. If ok, replace and program the Front Control Module.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

7. (D55) CAN B BUS (+) CIRCUIT FOR A SHORT TO GROUND




1. Turn the ignition off.
2. Disconnect the Front Control Module C1 harness connector.
3. Measure the resistance between ground and the (D55) CAN B Bus (+) circuit.

Is the resistance above 1000.0 Ohms?

Yes

- Go To 8

No

- Disconnect each CAN B Bus module one at a time while observing the resistance to determine if the short is caused by an internal short within a module. Replace the module,, that when disconnected eliminates the short to ground. If the short condition is still present with all CAN B Bus modules disconnected use the Wiring Diagrams to help isolate and repair the (D55) CAN B Bus (+) circuit for a short to ground.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

8. (D54) CAN B BUS (-) CIRCUIT FOR A SHORT TO GROUND




1. Measure the resistance between ground and the (D54) CAN B Bus (-) circuit.

Is the resistance above 1000.0 Ohms?

Yes

- Inspect the wiring and connectors for damage. If ok, replace and program the Front Control Module.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Disconnect each CAN B Bus module one at a time while observing the resistance to determine if the short is caused by an internal short within a module. Replace the module,, that when disconnected eliminates the short to ground. If the short condition is still present with all CAN B Bus modules disconnected use the Wiring Diagrams to help isolate and repair the (D54) CAN B Bus (-) circuit for a short to ground.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

9. (D55) CAN B BUS (+) CIRCUIT SHORTED TO THE (D54) CAN B BUS (-) CIRCUIT




1. Turn the ignition off.
2. Disconnect the Front Control Module C1 harness connector.
3. Measure the resistance between the (D55) CAN B Bus (+) circuit and (D54) CAN B Bus (-) circuit.

Is the resistance below 10K Ohms?

Yes

- Disconnect each CAN B Bus module one at a time while observing the resistance to determine if the short is caused by an internal short within a module. Replace the module,, that when disconnected eliminates the short between the two circuits. If the short condition is still present with all CAN B Bus modules disconnected, use the Wiring Diagrams to help isolate and repair the (D55) CAN B Bus (+) circuit for a short to the (D54) CAN B Bus (-) circuit.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Inspect the wiring and connectors for damage. If ok, replace and program the Front Control Module.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

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