Circuit Description
Modules connected to the controller area network (CAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. If no communication is detected on CAN serial data circuit, the DTC is set. A total non communication condition may be caused by a short to battery or voltage on any of the CAN circuits or a short between the CAN high and low circuits.
The following modules communicate on CAN serial data bus:
| • | The body control module (BCM) |
| • | The electronic brake control module (EBCM), if equipped |
| • | The engine/powertrain control module (ECM/PCM) |
| • | The transmission control module (TCM), with L61 |
DTC Descriptor
This diagnostic procedure supports the following DTCs:
| • | DTC U2102 More Controllers On Bus Than Programmed |
| • | DTC U2103 Fewer Controllers On Bus Than Programmed |
Conditions for Running the DTC
| • | Voltage supplied to the modules is in the normal operating voltage range. |
| • | The vehicle power mode requires communication to occur. |
Conditions for Setting the DTC
Each controller on the CAN serial data circuit monitors the activity or traffic on the bus. The modules have prerecorded information about what messages should be expected during normal functionality. The module setting the DTC does not receive CAN messages from all of the modules it expected to, or receives too many CAN messages. This indicates that there may be fewer controllers or more controllers actively communicating on the bus than programmed.
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) turns ON during the second consecutive drive cycles with the error detected in the ECM. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The ECM records the operating conditions at the time of turning ON the MIL and stores the data as Freeze Frame information. |
Conditions for Clearing the MIL/DTC
| • | A current DTC and MIL clear when the malfunction is no longer present. |
| • | A history DTC clears when requested by the scan tool or when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction. |
Step | Action | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Data Communication Schematics Connector End View Reference: Data Communication Connector End Views | |||||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |||||||||||
2 |
Did you record any of the following DTCs, with a current status?
| Go to Step 3 | |||||||||||
3 | Attempt to communicate with all modules that communicate on CAN bus, conform to vehicle options. See circuit description for the list of modules and options. Does the scan tool communicate with all modules that communicate on CAN bus? | Go to Step 4 | Go to Data Link References for the appropriate loss of communication procedure | ||||||||||
4 |
Is the DTC U2102 or U2103 still current? | Go to Step 5 | Go to Step 6 | ||||||||||
5 | Replace the control module that had set DTC U2102 or U2103. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | Go to Step 6 | -- | ||||||||||
6 |
Does the DTC reset? | Go to Step 1 | System OK | ||||||||||
