For 1990-2009 cars

### Circuit Description

Modules that are connected to the shared communication circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have pre-recorded information about what messages are needed to be exchanged on the serial data circuits for each virtual network. The messages are usually supervised and some periodic messages are used by the receiver module as an availability indication of the transmitter module.

### DTC Descriptors

This diagnostic procedure supports the following DTC:

DTC U0101 Lost Communication With Transmission Control Module (TCM)

### Conditions for Running the DTCs

• | The ignition is ON.

• | The DTC U0101 diagnostic runs continuously when the above condition is met.

### Conditions for Setting the DTC

The engine control module (ECM) cannot communicate with the TCM.

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

### Conditions for Clearing the MIL/DTC

• | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• | A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Test Description

The numbers below refer to the step numbers in the diagnostic table.

1. When the ECM stores a DTC U0101, a DTC U2105 simultaneously sets in the TCM. Performing the diagnostic procedures in DTC U2105 will repair DTC U0101.

Step | Action | Yes | No
--- | --- | --- | ---
1 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Use the scan tool and check for DTCs.

Is DTC U0101 present?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 2

2 | Does the scan tool communicate with the engine control module (ECM) and transmission control module (TCM)? | Go to Diagnostic System Check - Vehicle | Go to Scan Tool Does Not Communicate with CAN Device