The engine control module (ECM) creates the vehicle speed output signal by pulsing the vehicle speed signal circuit to ground at a rate of 4 KPPM. The VSS input is pulled high to B+ in the instrument panel cluster (IPC). The IPC converts the 4 KPPM vehicle speed signal to a speedometer position to indicate the vehicle speed. The ECM monitors the voltage at the vehicle speed signal circuit to determine when the voltage is out of the normal operating range.

The ECM records the operating conditions at the time the diagnostic fails. The ECM displays the failure information in the Failure Records on the scan tool.

Schematic Reference

Instrument Cluster Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Instrument Cluster Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

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

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.

1. Ignition OFF, disconnect the X1 harness connector at the radio.
2. Start the engine, with the drive wheels raised and the vehicle placed in drive or the first gear. Verify that the speedometer value does not match the scan tool Vehicle Speed parameter in the ECM Engine Data List.

⇒	If the speedometer matches the scan tool Vehicle Speed parameter, test the vehicle speed signal circuit terminal F2 for a short to voltage, a short to ground or an open/high resistance. If circuit tests normal, replace the radio.

3. Ignition OFF, disconnect the harness connector at the rear object sensor control module.
4. Start the engine, with the drive wheels raised and the vehicle placed in drive or the first gear. Verify that the speedometer value does not match the scan tool Vehicle Speed parameter in the ECM Engine Data List.

⇒	If the speedometer matches the scan tool Vehicle Speed parameter, test the vehicle speed signal circuit terminal 18 for a short to voltage, a short to ground or an open/high resistance. If circuit tests normal, replace the rear object sensor control module.

5. Ignition OFF, disconnect the harness connector at the head-up display (HUD).
6. Start the engine, with the drive wheels raised and the vehicle placed in drive or the first gear. Verify that the speedometer value does not match the scan tool Vehicle Speed parameter in the ECM Engine Data List.

⇒	If the speedometer matches the scan tool Vehicle Speed parameter, test the vehicle speed signal circuit terminal 11 for a short to voltage, a short to ground or an open/high resistance. If circuit tests normal, replace the HUD.

7. Ignition OFF disconnect the X1 harness connector at the engine control module.
8. Ignition ON, test for 9-11 volts between the vehicle speed signal circuit terminal 39 and ground.

⇒	If less than 9 volts, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the IPC.

⇒	If greater than 11 volts, test the signal circuit for a short to voltage. If the circuit tests normal, replace the IPC.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for the ECM, IPC, HUD, radio and rear object sensor control module replacement, setup and programming