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.

### Circuit/System Description

The instrument panel cluster (IPC) displays the vehicle speed based on the information from the body control module (BCM). The ECM 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.

### Reference Information

#### Schematic Reference

• | Instrument Cluster Schematics

• | Engine Controls Schematics

#### Connector End View Reference

• | Displays and Gages Connector End Views .

• | Engine Control Module Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Scan Tool Data List

### Circuit/System Testing

Important: The drive wheels of the vehicle must be raised and the transmission must be placed in drive or first gear.

Start the engine, raise the vehicle drive wheels and place the transmission in drive or first gear. Verify that the speedometer value matches the scan tool Vehicle Speed parameter in the ECM Engine Data List.

⇒ | If the speedometer is incorrect, test or replace the IPC.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for IPC replacement, setup, and programming