Speedometer and/or Odometer Inaccurate or Inoperative

Speedometer and/or Odometer Inaccurate or Inoperative (4.2L Engine)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using the diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

Circuit Description

The engine control module (ECM) creates the vehicle speed signal by pulsing the vehicle speed signal circuit to ground at a rate of 4KPPM. The instrument panel cluster (IPC) converts the 4KPPM vehicle speed signal to a speedometer position to indicate the vehicle speed. The IPC also receives from the ECM a serial data message indicating the vehicle speed. The IPC uses the serial data vehicle speed information from the ECM for diagnostics purposes. The ECM monitors the voltage on the vehicle speed signal circuit and determines when the voltage is out of the normal operating range.

Reference Information
Schematic Reference

Instrument Cluster Schematics (Instrument Cluster Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

* Instrument Cluster Description and Operation (Description and Operation)
* Engine Control Module Description (Engine Control Module Description)

Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

Important: The drive wheels of the vehicle must be raised and the transmission must be placed in drive or first gear. Refer to Lifting and Jacking the Vehicle (Service and Repair).


* Ignition ON, perform the speedometer sweep test with the scan tool. Verify that the speedometer gage sweeps from its low to high position.

• If the speedometer gage does not sweep from its low to high position, replace the IPC.

* Start the engine with the scan tool installed, the vehicle drive wheels raised and the transmission placed in drive or the first gear. Verify the speedometer display matches the scan tool Vehicle Speed parameter in the ECM Engine Data List.

Circuit/System Testing

1. Ignition OFF, disconnect the X1 harness connector at the ECM. Install a signal generator and instrument panel tester between the vehicle speed signal circuit terminal 39 and ground.
2. Ignition ON, set the signal generator to generate a speedometer signal. Verify that the vehicle speedometer indicates a reading.

• If no speedometer reading is present, test the signal circuit for a short to voltage, a short to ground or an open/high resistance. If the circuit tests normal, replace the instrument panel cluster (IPC).

3. If all circuits test normal, test or replace the ECM.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

Control Module References (Programming and Relearning) for the IPC replacement, setup, and programming