Speedometer and/or Odometer Inaccurate or Inoperative

SPEEDOMETER AND/OR ODOMETER INACCURATE OR INOPERATIVE

DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
The instrument panel cluster (IPC) displays the vehicle speed based on the information from the body control module (BCM). The engine control module (ECM) converts the data from the vehicle speed sensor to a 4,000 pulses/mile signal. The ECM then sends the vehicle speed signal information via the GMLAN serial data circuit to the BCM. The BCM sends a GMLAN message to the IPC indicating the vehicle speed. The IPC displays the vehicle speed based on the GMLAN serial data message from the BCM.

CIRCUIT/SYSTEM TESTING
1. Install a scan tool.
2. Raise the vehicle drive wheels.
3. Start the engine.
4. Place the transmission into drive.
5. With the scan tool, observe the Vehicle Speed Sensor (VSS) parameter in the ECM Engine Data list.
- If the VSS parameter does not match the speedometer display, replace the instrument panel cluster.
- If the odometer is not operating properly, replace the instrument panel cluster.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

Control Module References for IPC replacement, setup, and programming