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Body Control Module (BCM)






U0002-00-CAN C BUS OFF PERFORMANCE





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

Theory of Operation

The primary communication network between electronic control modules is the Controller Area Network (CAN) data bus system. The Controller Area Network (CAN) data bus allows all electronic modules connected to the bus to share information with each other. Regardless of whether a message originates from a module on the higher speed CAN C (500K) Bus or on the lower speed bus, CAN Interior High Speed (IHS) (125K) Bus, the message structure and layout is similar, which allows the Body Control Module/Central GateWay (BCM or BCMCGW) to process and transfer messages between the CAN buses. An additional gateway module, the Telematics Gateway (TGW) Module is used to transfer messages between the CAN IHS (125K) Bus and the CAN Audio and Telematics (AT) Bus. The BCM stores Diagnostic Trouble Codes (DTCs) for certain bus network faults on the CAN C (500K) Bus and CAN IHS (125K) Bus. The TGW stores DTCs for certain bus network faults on the CAN AT Bus.

All modules transmit and receive messages over one of these buses. Data exchange between the modules is achieved by serial transmission of encoded data messages (a form of transmission in which data bits are sent sequentially, one at a time, over a single line). Each module can both send and receive serial data simultaneously. Each data bit of a CAN Bus message is carried over the bus as a voltage differential between the two bus circuits which, when strung together, form a message. Each module uses arbitration to sort the message priority if two competing messages are attempting to be broadcast at the same time. Corruption of a single bit within a message will corrupt the entire message. Each message contains a Cyclic Redundancy Check (CRC) which specifies the message size exactly. If the message detected conflicts with the CRC the ECU receiving it will determine the message to be an error and consider that communication has not been possible. Diagnosis of this condition using a lab scope may reveal activity that appears to be Bus data messages even if no actual communication is possible. Communication problems that affect the whole bus, as a result of opens and terminal push outs are more likely to occur on data busses that operate at a high speed than a data bus that operates at a lower speed.

When an open circuit or terminal push out occurs one or more modules can become isolated from the remainder of the bus. The isolated module will attempt to communicate, but will not be able to receive messages or determine arbitration from other modules. Each time the isolated module attempts to communicate it alters the bus voltage on the intact bus circuit. Without functioning arbitration the isolated module alters the bus voltage while other bus messages are being sent thereby corrupting the messages on the remainder of the bus.

The CAN bus modules are connected in parallel to the two-wire bus using a twisted pair, where the wires are wrapped around each other to provide shielding from unwanted electromagnetic induction, thus preventing interference with the relatively low voltage signals being carried through them. While the CAN bus is operating (active), one of the bus wires will carry a higher voltage and is referred to as the CAN High or CAN bus (+) wire, while the other bus wire will carry a lower voltage and is referred to as the CAN Low or CAN bus (-) wire.

- When Monitored:
With the ignition on.

- Set Condition:
The Body Control Module (BCM) detects a short condition on one of the CAN C Bus circuits.





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

Does the scan tool display U0002-00-CAN C BUS OFF PERFORMANCE?

Yes

- Go To 2

No

- Test complete, the condition or conditions that originally set this DTC are not present at this time. Using the wiring diagrams as a guide, check all related splices and connectors for signs of water intrusion, corrosion, pushed out or bent terminals, and correct pin tension.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

2. CHECK THE CAN BUS (-) CIRCUIT FOR A SHORT TO VOLTAGE




1. Disconnect the scan tool.
2. Measure the voltage between ground and the CAN C Bus (-) circuit.

Is the voltage above 10.0 volts?

Yes

- Diagnose the short to voltage in the CAN C Bus (-) circuit. This measurement will need to be repeated in the following steps. Go To 5

No

- Go To 3

3. CHECK THE CAN C BUS (+) CIRCUIT FOR A SHORT TO GROUND




1. Measure the voltage between ground and the CAN C Bus (+) circuit.

Is the voltage approximately 0 volt?

Yes

- Diagnose the short to ground in the CAN C Bus (+) circuit. This measurement will need to be repeated in the following steps. Go To 5

No

- Go To 4

4. CHECK FOR A SHORT BETWEEN THE CAN C BUS (+) CIRCUIT AND CAN C BUS (-) CIRCUIT




1. Measure the voltage between ground and the CAN C Bus (+) circuit.
2. Measure the voltage between ground and the CAN C Bus (-) circuit.

Are both values approximately 2.45 volts?

Yes

- Diagnose the short between the CAN C Bus (+) circuit and the CAN C Bus (-) circuit. This measurement will need to be repeated in the following steps. Go To 5

No

- Test complete, the condition or conditions that originally set this DTC are not present at this time. Using the wiring diagrams as a guide, check all related splices and connectors for signs of water intrusion, corrosion, pushed out or bent terminals, and correct pin tension.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

5. ISOLATE THE CONCERN USING THE STAR CONNECTORS
1. Turn the ignition off.
2. Disconnect the Rear CAN C Star Connector C1 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- The concern is related to the modules or circuits connected to the Front CAN C Star Connector. Go To 6

No

- The concern is related to the modules or circuits connected to the Rear CAN C Star Connector. Go To 14

6. CHECK THE CAN C BUS CIRCUITS BETWEEN THE STAR CONNECTORS
1. Turn the ignition off.
2. Disconnect the Front CAN C Star Connector C1 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Go To 7

No

- Repair the short in the CAN C bus circuits between the Front CAN C Star Connector and the Rear CAN C Star Connector.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

7. CHECK THE POWERTRAIN CONTROL MODULE CAN C BUS CIRCUITS
1. Turn the ignition off.
2. Disconnect the Front CAN C Star Connector C7 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Go To 8

No

- Diagnose the wiring and connectors between the Front CAN C Star Connector and the PCM for damage or shorted circuits. If OK, replace and program the Powertrain Control Module. Powertrain Control Module - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

8. CHECK THE ANTILOCK BRAKE MODULE CAN C BUS CIRCUITS
1. Turn the ignition off.
2. Disconnect the Front CAN C Star Connector C6 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Go To 9

No

- Diagnose the wiring and connectors between the Front CAN C Star Connector and the ABS Module. If OK, replace and program the Antilock Brake Module. Anti-Lock Brake System Module - Removal.
- Perform the ABS VERIFICATION TEST. ABS Verification Test.

9. CHECK THE OCCUPANT RESTRAINT CONTROLLER MODULE CAN C BUS CIRCUITS
1. Turn the ignition off.
2. Disconnect the Front CAN C Star Connector C2 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Go To 10

No

- Diagnose the wiring and connectors between the Front CAN C Star Connector and the ORC Module. If OK, replace the Occupant Restraint Controller Module. Occupant Restraint Controller - Removal.
- Perform the RESTRAINTS SYSTEM VERIFICATION TEST. Restraints System Verification Test.

10. CHECK THE STEERING CONTROL MODULE (SCM)/STEERING COLUMN CONTROL MODULE (SCCM) CAN C BUS CIRCUITS
1. Turn the ignition off.
2. Disconnect the Front CAN C Star Connector C4 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Go To 11

No

- Diagnose the wiring and connectors between the Front CAN C Star Connector and the SCM/SCCM. If OK, replace the Steering Control Module. Steering Column Module - Removal.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

11. CHECK THE INSTRUMENT CLUSTER (IC) CAN C BUS CIRCUITS
1. Turn the ignition off.
2. Disconnect the Front CAN C Star Connector C5 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Go To 12

No

- Diagnose the wiring and connectors between the Front CAN C Star Connector and the IC. If OK, replace the Instrument Cluster. Instrument Cluster - Removal.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

12. CHECK THE TRANSMISSION CONTROL MODULE (TCM) CAN C BUS CIRCUITS

NOTE: If vehicle is not equipped with this module, answer yes to the question.

1. Turn the ignition off.
2. Disconnect the Front CAN C Star Connector C8 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Go To 13

No

- Diagnose the wiring and connectors between the Front CAN C Star Connector and the TCM. If OK, replace the Transmission Control Module (TCM).
- Perform the BODY VERIFICATION TEST. Body Verification Test.

13. CHECK THE DATA LINK CONNECTOR (DLC) CAN C BUS CIRCUITS
1. Turn the ignition off.
2. Disconnect the Front CAN C Star Connector C3 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Repair the short in the CAN C bus circuits between the Front CAN C Star Connector and the DLC.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Reconnect all the connectors and retest. If the concern is still present, replace the Front Star Connector.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

14. CHECK THE BODY CONTROL MODULE (BCM) CAN C BUS CIRCUITS
1. Turn the ignition off.
2. Reconnect the Rear CAN C Star Connector C1 harness connector.
3. Disconnect the Rear CAN C Star Connector C2 harness connector.
4. Turn the ignition on.
5. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Go To 15

No

- Diagnose the wiring and connectors between the Rear CAN C Star Connector and the BCM. If OK, replace the Body Control Module (BCM). Body Control Module - Removal.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

15. CHECK THE TIRE PRESSURE MONITORING (TPM) MODULE CAN C BUS CIRCUITS
1. Turn the ignition off.
2. Disconnect the Rear CAN C Star Connector C3 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Go To 16

No

- Diagnose the wiring and connectors between the Rear CAN C Star Connector and the TPM. If OK, replace the Tire Pressure Monitoring (TPM) Module. Tire Pressure Monitoring (TPM) Module - Removal.
- Perform the TPM VERIFICATION TEST. Tire Pressure Monitor (TPM) Verification Test.

16. CHECK THE RADIO FREQUENCY HUB (RFH) MODULE CAN C BUS CIRCUITS
1. Turn the ignition off.
2. Disconnect the Rear CAN C Star Connector C5 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Go To 17

No

- Diagnose the wiring and connectors between the Rear CAN C Star Connector and the RFH. If OK, replace the Radio Frequency (RF) Hub Module. Radio Frequency Module (RF Hub) - Removal.
- Perform the RADIO FREQUENCY HUB (RF HUB) VERIFICATION TEST. RF Hub Verification Test.

17. CHECK THE DRIVE TRAIN CONTROL MODULE CAN C BUS CIRCUITS
1. Turn the ignition off.

NOTE: If vehicle is not equipped with this module, answer yes to the question.

2. Disconnect the Rear CAN C Star Connector C6 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Go To 18

No

- Diagnose the wiring and connectors between the Rear CAN C Star Connector and the DTCM. If OK, replace the Drive Train Control Module (DTCM). Drivetrain Control Module - Removal.
- Perform the DTCM VERIFICATION TEST. DTCM Verification Test.

18. CHECK THE PARK ASSIST MODULE CAN C BUS CIRCUITS
1. Turn the ignition off.

NOTE: If vehicle is not equipped with this module, answer yes to the question.

2. Disconnect the Rear CAN C Star Connector C4 harness connector.
3. Turn the ignition on.
4. Repeat the measurement at the DLC.

Is the concern still present?

Yes

- Reconnect all the connectors and retest. If the concern is still present, replace the Rear Star Connector.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Diagnose the wiring and connectors between the Rear CAN C Star Connector and the PTS. If OK, replace the Park Assist Module. Park Assist Module - Removal.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

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