U2172

DTC U2105-U2199

Circuit Description

The controller area network (CAN) serial data line is a high speed serial data bus used to communicate information between the engine control module (ECM), body control module (BCM), and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure the required real-time response is maintained. The CAN serial data line does not communicate with the scan tool via the data link connector (DLC). CAN serial data information is interpreted by the BCM and transmitted to the serial data line by the BCM.




The CAN bus is continuously monitored by the serial data bus. Each module on the CAN serial data circuit learns the identity of the other modules on the circuit. If a module stops communicating after all modules have initiated for the igniting cycle, other module set a DTC specific for the module not communicating:

* DTC U2105, can not communicate with the ECM
* DTC U2106, can not communicate with the TCM
* DTC U2172, can not communicate with the Radio

DTC Descriptors

This diagnostic procedure supports the following DTCs:

* DTC U2105 Lost Communications With Engine Control System
* DTC U2199 Unassigned

Conditions for Running the DTC

* Supply voltage to the modules are in the normal operating range.
* The vehicle is in the RUN power mode.

Conditions for Setting the DTC

The module setting the DTC has attempted to establish communications on the CAN circuits for more than 7 times.

Action Taken When the DTC Sets

Besides storing the DTC as both current and history, and using default values for missing parameters, the modules on the CAN network each take separate actions as listed:

* ECM
- Turn ON the malfunction indicator lamp (MIL) during the second consecutive drive cycle with the error detected.
- Record the operating conditions at the time of turning ON the MIL and store the data as Freeze Frame information.

* TCM
Send a request to the ECM to turn ON the MIL during the second consecutive drive cycle with the error detected.

* BCM
- Turn ON the MIL during the second consecutive drive cycle with the error detected.
- Record the operating conditions at the time of turning ON the MIL and store the data as Freeze Frame information.

Conditions for Clearing the DTC

The MIL is cleared, turned OFF, and the DTC is cleared by a different strategy for each module.

* ECM
- If the fault is not detected 3 consecutive drive cycles, the current DTC is cleared and the MIL is turned OFF.
- The history DTC is cleared if the malfunction does not reoccur for 40 consecutive drive cycles.
- The history DTC is cleared if there is a keep alive memory (KAM) reset (battery disconnected).

* TCM
- If the fault is not detected one consecutive drive cycle, the current DTC is cleared.
- The history DTC is cleared if the malfunction does not reoccur for 40 consecutive drive cycles.

* BCM
- If the fault is not detected 3 consecutive drive cycles, the current DTC is cleared and the MIL is turned OFF.
- The history DTC is cleared if the malfunction does not reoccur for 40 consecutive drive cycles.
- The history DTC is cleared if there is a KAM reset, battery disconnected.

Test Description

Step 1 - Step 10:

The numbers below refer to the step numbers on the diagnostic table.
7. The module which was not communicating due to an open in the GMLAN serial data circuits may have set Loss of Communication DTCs for those modules that it was monitoring.
9. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.