Body Control Module (BCM)

U0001-87-CAN C BUS - NO SIGNAL





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

Theory of Operation

The Body Control Module (BCM) provides the central connection point for vehicle communication. The BCM is the only module connected to both the CAN B and CAN C buses. The scan tool uses only the CAN C Bus to communicate with the BCM. The scan tool communicates directly with each of the CAN B modules. The BCM serves as the CAN B star connection point and provides a wire harness in-line connection for the scan tool CAN B diagnostics.

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 B (50K) 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. The BCM stores Diagnostic Trouble Codes (DTCs) for certain bus network faults on the CAN C (500K) Bus and CAN B (50K) Bus.

The CAN C bus modules are connected in series, and the CAN B bus modules are connected in parallel. Both use a 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.

A short to ground or voltage on either of the CAN C bus circuits will prevent the CAN C modules from communicating. For the CAN B bus, a short to ground or voltage on only one bus circuit will not prevent the modules from communicating.

- When Monitored:
With the ignition on.

- Set Condition:
The module detects an open condition on one of the CAN C Bus circuits.





Diagnostic Test

1. CHECK FOR AN ACTIVE DTC

NOTE: Prior to diagnosing this DTC, check the module connectors for signs of water intrusion, corrosion, pushed out or bent terminals, and correct pin tension.

1. Turn the ignition on.
2. With the scan tool, read DTCs.

Does the scan tool display this DTC as active?

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 C BUS (+) CIRCUIT FOR AN OPEN OR HIGH RESISTANCE
1. Turn the ignition off.
2. Disconnect the BCM C1 harness connector.
3. Disconnect the Electric Power Steering (EPS) harness connector.

NOTE:
Inspect the BCM & EPS harness connector female pins carefully for internal spread terminals.

4. Measure the resistance of the CAN C Bus (+) circuit between the BCM C1 and EPS harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Go To 3

No

- Repair the CAN C Bus (+) circuit for an open or high resistance.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

3. CHECK THE CAN C BUS (-) CIRCUIT FOR AN OPEN OR HIGH RESISTANCE
1. Turn the ignition off.
2. Measure the resistance of the CAN C Bus (-) circuit between the BCM C1 and EPS harness connector.

Is the resistance above 5.0 Ohms?

Yes

- Repair the CAN C Bus (-) circuit for an open or high resistance.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Replace the Body Control Module (BCM). Body Control Module - Removal.
- Perform the BODY VERIFICATION TEST. Body Verification Test.