For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P0864: TCM Communication Circuit Performance

### Circuit/System Description

The transmission control module (TCM) sends vehicle speed data to the engine control module (ECM). The data is sent to the ECM through a high speed network called the GM control area network (CAN). Two circuits are used to communicate CAN data between the ECM and TCM. A fault in the CAN will not cause DTC P0864 to set by itself. If a CAN fault occurs, other DTCs set before DTC P0864.

### Conditions for Running the DTC

• | The ignition is ON for more than 3 seconds.

• | The ignition voltage is between 10-18 volts.

• | No other CAN errors are present.

• | DTC P0864 runs continuously once the above conditions are met.

### Conditions for Setting the DTC

The ECM receives no valid vehicle speed data from the TCM for more than 1 second.

### Action Taken When the DTC Sets

DTC P0864 is a type A DTC.

### Conditions for Clearing the DTC

DTC P0864 is a type A DTC.

### Reference Information

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

Important: Record all Failure Records before clearing the DTC. Using Clear Info erases the Failure Records from the engine control module (ECM) and transmission control module (TCM).

1. Ignition ON, record the DTC Freeze Frame/Failure Records.

⇒ | If any TCM Freeze Frame/Failure Records are recorded refer to Diagnostic Trouble Code (DTC) List - Vehicle .

2. Clear the DTC information with a scan tool.
3. Ignition OFF for at least 30 seconds.
4. Engine idling for 1 minute. DTC P0864 should not set.

⇒ | If DTC P0864 sets and no TCM DTCs are present, replace the ECM.

⇒ | If DTC P0864 and TCM DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for engine control module replacement, setup, and programming