The transmission control module (TCM) sends vehicle speed data to the engine control module (ECM). The data is sent to the ECM through a communication network called the GM local area network (LAN). Two circuits are used to communicate LAN data between the ECM and TCM.

The ignition is ON.

The ECM receives no valid vehicle speed data from the TCM.

DTC P1504 is a type A DTC.

DTC P1504 is a type A DTC.

Schematic Reference

Engine Controls Schematics

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the DTC information with a scan tool. Verify no DTCs are set

⇒	If any other DTCs set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Attempt to communicate with the TCM with a scan tool.

⇒	If the scan tool is unable to communicate with the TCM, test the communication circuits between the TCM and the ECM for an open/high resistance. If the circuits test normal, replace the TCM.

3. Clear the scan tool DTC information parameter. Engine running, observe the scan tool DTC information parameter. Verify DTC P1504 sets this ignition cycle.

⇒	If DTC P1504 sets this ignition, test the communication circuits between the TCM and the ECM for an open/high resistance. If the circuits test normal, replace the ECM.

4. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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