For 1990-2009 cars

### 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 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

### Conditions for Running the DTC

The CAN circuits are monitored continuously by the modules on the circuit.

### 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, 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).

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 |

1. Install the scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With the scan tool, communicate with the body control module (BCM), engine control module (ECM), and transmission control module (TCM).
4. Monitor the DTC information for DTC U2100.
5. Monitor the DTC information for DTCs in the range of U2102-U2104.

Does the scan tool indicate that DTC U2100 or DTCs in the range of U2102-U2104 as either current or history DTCs?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3 |

1. Test all battery positive and ignition positive circuits of the module that is not communicating for opens or shorts to ground.
2. Test all grounds of the module that is not communicating for opens.

Did you find and correct the concern?

Go to Step 4

Go to Step 5

4 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition switch.
3. Wait at least 10 seconds.
4. Turn the ignition ON, with the engine OFF.
5. Retrieve DTCs from the ECM, TCM, and BCM.

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 CAN circuits. Did you find and correct the concern? | Go to Step 4 | Go to Step 6
6 | Inspect for poor connections at the harness connector of the module that is not communicating. Did you find and correct the condition? | Go to Step 7 | Go to Step 10
7 | Inspect the connector of the module recording the DTC. Did you find and correct the condition? | Go to Step 8 | Go to Step 9
8 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition switch.
3. Wait at least 10 seconds.
4. Turn the ignition ON, with the engine OFF.
5. Retrieve the DTCs from the ECM, TCM, and BCM.

Does the DTC reset?

Go to Step 2

System OK

9 | Important: Perform the programming or set up procedure for the replaced control module if required. Replace the control module that has set the DTC. Refer to Control Module References in Body Control System for the applicable replacement procedure.

Did you complete the replacement?

Go to Step 8

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10 | Important: Perform the programming or set up procedure for the replaced control module if required. Replace the control module that is not communicating. Refer to Control Module References in Body Control System for the applicable replacement procedure.

Did you complete the replacement?

Go to Step 4

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