For 1990-2009 cars
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

### Circuit Description

The engine control module (ECM) functions as the central module for the controller area network (CAN) bus. The CAN consists of two separate conductors between the ECM and the transmission control module (TCM). Two additional conductors connect the ECM and the Electronic Brake/Traction Control Module (EBTCM). Each module sends information by toggling the circuits high or low to produce pulse-width signals, which the other modules decode.

The CAN data stream contains information such as status messages for relevant operating parameters, device requests and acknowledgments, and state-of-health messages.

When the TCM has not received EBTCM data for a specified amount of time, then DTC U2108 will set. DTC U2108 is a type C DTC.

### Condition for Running the DTC

The ignition is ON.

### Condition for Setting the DTC

The TCM has not received EBTCM messaging for 1 second.

### Action Taken When the DTC Sets

• | The TCM does not request the ECM to illuminate the MIL.

• | The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM records this information as Failure Records.

• | The TCM stores DTC U2108 in TCM history.

### Conditions for Clearing the DTC

• | A scan tool can clear the DTC.

• | The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring.

• | The TCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the TCM.

### Test Description

The number below refers to the step number on the diagnostic table.

1. Performing this step verifies that an operational abnormality did not take place during TCM power-up, such as Electromagnetic Interference (EMI).

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission ? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission
2 |

1. Install the Scan Tool .
2. Turn ON the ignition with the engine OFF.

Important: Record the Failure Records before clearing the DTCs. Using the Clear Info function erases the Failure Records from the ECM and the TCM.

3. Record the DTC Failure Records.
4. Clear the DTC.
5. Turn OFF the ignition for at least 30 seconds.
6. Turn ON the ignition with the engine OFF.

Did DTC U2108 reset?

--

Go to Step 3

Go to Intermittent Conditions in Engine Controls

3 | Did you record a Failure Record for DTC U2100? | -- | Go to DTC U2100 | Go to Step 4
4 | Did you record a Failure record for any EBTCM DTCs? | -- | Go to the applicable EBTCM DTC | Go to Step 5
5 | Replace the EBTCM. Refer to Electronic Brake Control Module Replacement in Antilock Brake System. Is the action complete? | -- | Go to Step 6 | --
6 | Perform the following procedure in order to verify the repair:

1. Select DTC.
2. Select Clear Info.
3. Start the engine.

Did DTC U2108 reset?

--

Go to Step 1

System OK