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 |
Control Module | ID Number |
|---|---|
Engine Control Module (ECM) | 05 |
Transmission Control Module (TCM) | 06 |
Radio | 72 |
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 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
The numbers below refer to the step numbers on the diagnostic table.
-
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.
-
The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
Step | Action | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems | |||||||||||||||
1 | Did you perform the Diagnostic System Check for the system exhibiting the symptom? | Go to Step 2 | Go to Control Module References in Body Control System for the applicable Diagnostic System Check | ||||||||||||
2 |
Refer to Data Link Connector Schematics for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 9 | Go to Step 3 | ||||||||||||
3 | Test the ground circuits of the module that is not communicating for an open. Refer to Data Link Connector Schematics for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 9 | Go to Step 4 | ||||||||||||
4 | Test the GMLAN serial data circuits of the module that is not communicating for an open. Refer to Data Link Connector Schematics for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 7 | Go to Step 5 | ||||||||||||
5 | Test the following circuits of the module that is not communicating for poor connections:
Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 9 | Go to Step 6 | ||||||||||||
6 |
Important: Perform the module setup procedure if required. Replace the module that is not communicating. Refer to Control Module References in Body Control Systems. Did you complete the replacement? | Go to Step 9 | -- | ||||||||||||
Does the scan tool display any DTCs which do not begin with a "U"? | Go to the Control Module References for the applicable Diagnostic System Check | Go to Step 8 | |||||||||||||
8 | Use the scan tool in order to clear the DTCs. Did you complete the action? | Go to Step 9 | -- | ||||||||||||
Select the Display DTCs function for the modules which had the Loss of Communications DTC set. Does the scan tool display any DTCs which do not begin with a "U"? | Go to the Control Module References for the applicable Diagnostic System Check | Go to Step 10 | |||||||||||||
10 |
Did you complete the action? | System OK | -- | ||||||||||||
