U0019-01
U0019-01-CAN B BUS - GENERAL ELECTRICAL FAILURE
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 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.
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 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.
- When Monitored:
Continuously.
- Set Condition:
The Body Control Module (BCM) detects that the CAN B Bus (+) or CAN Bus (-) circuit is open, shorted to voltage, shorted to ground, or are shorted together.
1. TEST FOR INTERMITTENT CONDITION
NOTE: Check for any Technical Service Bulletins (TSBs) related to the condition. If a TSB applies, perform the procedure outlined in the TSB before continuing.
1. Turn the ignition on.
2. Using the scan tool, record and erase DTCs.
3. Cycle the ignition from on to off three times.
4. Turn the ignition on.
5. Using 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. MEASURE VOLTAGE AT THE DLC
1. Disconnect the scan tool.
2. Measure the voltage between ground and the CAN B Bus circuits.
Does the voltage read approximately 4.65 - 4.98 volts on the (D42) CAN B Bus (-) and 0.39 - 0.46 volts on the (D41) CAN B (+) circuits?
Yes
- Go To 3
No - Voltage Between 0.3 - 0.7 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. CHECK THE (D41) CAN B BUS (+) CIRCUIT FOR AN OPEN
1. Turn the ignition on.
2. Reconnect the scan tool.
3. With the scan tool, view the modules.
4. Using a fused jumper wire, connect one end to ground and with the other end backprobe the (D41) CAN B Bus (+) circuit at the DLC harness connector.
NOTE: This may cause some modules to no longer communicate on the Bus.
Are some modules no longer communicating?
Yes
- Using the Wiring Diagrams to further isolate the open in the circuit, repair the (D41) CAN B Bus (+) circuit for an open.
- Perform the BODY VERIFICATION TEST. Body Verification Test.
No
- Go To 4
4. CHECK THE (D42) CAN B BUS (-) CIRCUIT FOR AN OPEN
1. Remove the fused jumper wire.
2. Using a fused jumper wire, connect one end to ground and with the other end backprobe the (D42) CAN B Bus (-) circuit at the DLC harness connector.
NOTE: This may cause some modules to no longer communicate on the Bus.
Are some modules no longer communicating?
Yes
- Using the Wiring Diagrams to further isolate the open in the circuit, repair the (D42) 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 module that set this DTC.
- Perform the BODY VERIFICATION TEST. Body Verification Test.
5. CHECK THE (D41) CAN B BUS (+) CIRCUIT FOR A SHORT TO VOLTAGE
1. Turn the ignition off.
2. Disconnect the scan tool from the DLC.
3. Turn the ignition on.
4. Measure the voltage between the (D41) 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 (D41) CAN B Bus (+) circuit for a short to voltage.
- Perform the BODY VERIFICATION TEST. Body Verification Test.
No
- Go To 6
6. CHECK THE (D42) CAN B BUS (-) CIRCUIT FOR A SHORT TO VOLTAGE
1. Measure the voltage between the (D42) 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 (D42) 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 module that set this DTC.
- Perform the appropriate verification test for the module being replaced. If there is no verification test for the associated module perform the BODY VERIFICATION TEST. Body Verification Test.
7. CHECK THE (D41) CAN B BUS (+) CIRCUIT FOR A SHORT TO GROUND
1. Turn the ignition off.
2. Disconnect the scan tool from the DLC.
3. Measure the resistance between ground and the (D41) 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 (D41) CAN B Bus (+) circuit for a short to ground.
- Perform the BODY VERIFICATION TEST. Body Verification Test.
8. CHECK THE (D42) CAN B BUS (-) CIRCUIT FOR A SHORT TO GROUND
1. Measure the resistance between ground and the (D42) 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 module that set this DTC.
- Perform the appropriate verification test for the module being replaced. If there is no verification test for the associated 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 (D42) CAN B Bus (-) circuit for a short to ground.
- Perform the BODY VERIFICATION TEST. Body Verification Test.
9. CHECK THE (D41) CAN B BUS (+) CIRCUIT FOR A SHORT TO THE (D42) CAN B BUS (-) CIRCUIT
1. Turn the ignition off.
2. Disconnect the scan tool from the DLC.
3. Measure the resistance between the (D41) CAN B Bus (+) circuit and (D42) CAN B Bus (-) circuit.
Is the resistance below 1000.0 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 (D41) CAN B Bus (+) circuit for a short to the (D42) 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 module that set this DTC.
- Perform the appropriate verification test for the module being replaced. If there is no verification test for the associated module perform the BODY VERIFICATION TEST. Body Verification Test.