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

Connector End View Reference

Engine Controls Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

1. Ignition ON, observe the DTC information with a scan tool.

⇒	If the scan tool displays any other DTCs refer to Diagnostic Trouble Code (DTC) List - Vehicle .

2. With a scan tool attempt to communicate with the TCM.

⇒	If the scan tool is unable to communication with the TCM, refer to Scan Tool Does Not Communicate with High Speed GMLAN Device for further diagnosis.

3. Clear the DTC information with a scan tool. Engine idling, observe the DTC information with a scan tool. Verify that 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/connections test normal, replace the ECM.

4. If the vehicle passes the Circuit/System Verification test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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