Communications

U0021-CAN B BUS (+) CIRCUIT OPEN





For a complete wiring diagram Consult Diagrams/Electrical.

- When Monitored:
With the ignition on and battery voltage between 10 and 16 volts.

- Set Condition:
The FCM detects the (D55) CAN B Bus (+) circuit is open.





Diagnostic Test

1. TEST FOR INTERMITTENT CONDITION
Turn the ignition on.
With the scan tool, record and erase FCM DTC's
Cycle the ignition from on to off 3 times.
Turn the ignition on.
With the scan tool, read active FCM DTC's.
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. ATTEMPT TO ISOLATE THE OPEN CONDITION




Turn the ignition on.
Verify that all CAN B Bus modules are communicating with the scan tool.

NOTE: A red X will be next to the module that is not communicating, indicating that the module is not active on the Bus network. A green check indicates that the module is active on the Bus network.

NOTE: If any module is not communicating, perform the appropriate no response test procedure before proceeding.Communications - Verbose Codes

Turn the ignition off.
Gain access to the Front Control Module C1 harness connector, but do not disconnect.
Using a fused jumper wire, connect one end to ground and with the other end backprobe the CAN B Bus (-) circuit at the FCM C1 harness connector.
Turn the ignition on.
With the scan tool monitor the network status screen and document all modules that display a red X.
Are there any red X's displayed next to the modules?

Yes

- Go To 3

No

- Check backprobe connection to ground, make sure it is proper. The CAN B Bus open DTC may no longer be active, it may be stored. Check all module connections
- Perform BODY VERIFICATION TEST - VER 1.Body Verification Test.

3. ATTEMPT TO ISOLATE THE OPEN CONDITION - MULTIPLE RED X'S
With the scan tool continue monitoring the network status screen.
Are there multiple red X's displayed next to the modules?

Yes

- The most likely cause of this condition is an open CAN B Bus (+) circuit between a common CAN B Bus splice and the modules that display the red X next to them. Use the wiring diagrams will help you determine where open condition exists.
- Perform BODY VERIFICATION TEST - VER 1.Body Verification Test.

No

- Go To 4

4. (D55) CAN B BUS (+) CIRCUIT OPEN - SINGLE RED X
Turn the ignition off.
Disconnect the module that has the red X displayed next to it.
Turn the ignition on.
Measure the voltage between the (D55) CAN B Bus (+) circuit and ground.
Is there any voltage present?

Yes

- Inspect the connector and terminal for damage, inspect for spread terminals, or push out terminals. If ok, replace the module that displayed the red X next to it.
- Perform BODY VERIFICATION TEST - VER 1.Body Verification Test.

No

- Repair the (D55) CAN B Bus (+) circuit for an open between the next common splice and the module that has the red X displayed next to it. Use the wiring diagrams will help you determine where open condition exists.
- Perform BODY VERIFICATION TEST - VER 1.Body Verification Test.