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 that 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.
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 ignition cycle, other modules set a DTC U21XX, where XX is equal to the 2 digit identification number specific for the module not communicating:
| • | DTC U2105, can not communicate with the ECM |
| • | DTC U2106, can not communicate with the TCM |
| • | DTC U2107, can not communicate with the BCM |
Control Module | ID Number |
|---|---|
Engine Control Module (ECM) | 05 |
Transaxle Control Module (TCM) | 06 |
Body Control Module (BCM) | 07 |
DTC Descriptors
This diagnostic procedure supports the following DTCs:
DTC U21XX Lost Communications With XX Module
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 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. |
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 - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Does the scan tool indicate that DTC U2100 or DTCs in the range of U2102-U2104 are set as either current or history? | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | Go to Step 3 |
3 |
Did you find and correct the concern? | Go to Step 4 | Go to Step 5 |
4 |
Does the DTC reset? | Go to Step 7 | System OK |
5 | Test all CAN serial data circuits between the module setting the DTC and the module that is not communicating for opens, shorts to voltage, shorts to ground, and shorts between controller area network (CAN) circuits. Did you find and correct the concern? | Go to Step 8 | Go to Step 6 |
6 | Inspect for poor connections at the harness connector of the module that is not communicating or recording the DTC. Did you find and correct the condition? | Go to Step 8 | Go to Step 7 |
7 | Replace the control module that is not communicating or caused the DTC. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 8 | -- |
8 |
Does the DTC reset? | Go to Step 2 | System OK |
