Body Control Module (BCM)
U0010-00-CAN INTERIOR BUS
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. The BCM stores Diagnostic Trouble Codes (DTCs) for certain bus network faults on the CAN C (500K) Bus and CAN IHS (125K) Bus.
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.
For additional information on the communication network and star connector locations, Communication - Description.
- When Monitored:
With the ignition on.
- Set Condition:
The Body Control Module (BCM) detects that the CAN IHS Bus has been off for more than five seconds when activity was expected.
Diagnostic Test
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 and wait 10 seconds.
5. With the scan tool, read active 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 IHS BUS CIRCUITS FOR THE CAN IHS BUS (125K) MODULES
NOTE: When performing this step, turn the ignition off (wait one minute) before disconnecting any module. When the module is disconnected turn the ignition on.
NOTE: This step is to determine if the fault is a module or the circuits between the module and the Start Connector.
1. While monitoring the scan tool, disconnect each CAN IHS Bus (125K) module at the Front CAN IHS Star Connector (except for the BCM and DLC), one at a time.
2. Check for this DTC to become stored after disconnecting each CAN IHS Bus (125K) module the vehicle is equipped with.
NOTE: If the DTC becomes stored when a particular module is disconnected, that module or related circuits are causing the DTC to set.
With all the CAN IHS Bus modules disconnected at the Star Connector (except for BCM and DLC), does the scan tool display this DTC as active?
Yes
- Go To 3
No
- Diagnose the wiring and connectors between the Front CAN IHS Star Connector and the module that when disconnected caused this DTC to become stored for damage or shorted circuits. If OK, replace the module that when disconnected caused this DTC to become stored.
- Perform the BODY VERIFICATION TEST. Body Verification Test .
3. CHECK THE (D158) CAN IHS BUS (125K) (-) CIRCUIT FOR A SHORT TO VOLTAGE
1. Turn the ignition off.
2. Disconnect the scan tool.
3. Disconnect the Front CAN IHS Star Connector for the DLC.
4. Turn the ignition on.
5. Measure the voltage between ground and the (D158) CAN IHS Bus (125K) (-) circuit.
Is there any voltage present?
Yes
- Repair the short to voltage in the (D158) CAN IHS Bus (-) circuit.
- Perform the BODY VERIFICATION TEST. Body Verification Test .
No
- Go To 4
4. CHECK THE (D157) CAN IHS BUS (125K) (+) CIRCUIT FOR A SHORT TO GROUND
1. Turn the ignition off.
2. Measure the resistance between ground and the (D157) CAN IHS Bus (125K) (+) circuit.
Is the resistance above 10k Ohms?
Yes
- Go To 5
No
- Repair the short to ground in the (D157) CAN IHS Bus (125K) (+) circuit.
- Perform the BODY VERIFICATION TEST. Body Verification Test .
5. CHECK FOR A SHORT BETWEEN THE (D157) CAN IHS BUS (125K) (+) CIRCUIT AND (D158) CAN IHS BUS (125K) (-) CIRCUIT
1. Measure the resistance between the (D158) CAN IHS Bus (125K) (-) and the (D157) CAN IHS Bus (125K) (+) circuits.
Is the resistance above 10k Ohms?
Yes
- Go To 6
No
- Repair the short between the (D157) CAN IHS Bus (125K) (+) circuit and the (D158) CAN IHS Bus (125K) (-) circuit.
- Perform the BODY VERIFICATION TEST. Body Verification Test .
6. CHECK THE CAN IHS BUS CIRCUITS FOR BCM
1. Disconnect the Front CAN IHS Star Connector for the BCM.
2. Reconnect all other connectors.
3. Cycle the ignition from on to off three times.
4. Turn the ignition on and wait 10 seconds.
5. With the scan tool, read all DTCs.
Do any modules on the CAN IHS BUS (125K) display this DTC as active?
Yes
- Reconnect all the connectors and retest. If the concern is still present, replace the Star Connector.
- Perform the BODY VERIFICATION TEST. Body Verification Test .
No
- Diagnose the wiring and connectors between the Front CAN IHS 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 .