The engine control module (ECM) creates the vehicle speed output signal by pulsing the vehicle speed signal circuit to ground at a rate of 4KPPM. The ECM monitors the voltage at the vehicle speed output signal circuit to determine when the voltage is out of the normal operating range. The instrument panel cluster (IPC) receives vehicle speed data from the ECM via the serial data circuit for display in the speedometer. The radio, object detection module and the inside rearview mirror (ISRVM) receive vehicle speed data via a discreet vehicle speed signal circuit from the ECM. The radio, object detection module and the ISRVM use the 4KPPM vehicle speed signal from the ECM to determine vehicle speed.

Schematic Reference

Connector End View Reference

Electrical Information Reference

Scan Tool Reference

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 does not match 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 ON, with the scan tool installed, perform the IPC Gage Sweep Test in the IPC Output Controls. Verify the speedometer dial moves from the minimum to the maximum position and back to the speedometer minimum position.

⇒	If the speedometer does not perform the IPC Gage Sweep Test, replace the IPC.

2. Ignition OFF, disconnect the C4 harness connector at the radio.
3. 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 for a short to voltage, a short to ground or an open/high resistance. If circuit tests normal, replace the radio.

4. Ignition OFF, disconnect the harness connector at the rear object detection control module.
5. 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 for a short to voltage, a short to ground or an open/high resistance. If circuit tests normal, replace the object detection control module.

6. Ignition OFF, disconnect the harness connector at the inside rearview mirror (ISRVM).
7. 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 for a short to voltage, a short to ground or an open/high resistance. If circuit tests normal, replace the ISRVM.

8. Ignition OFF disconnect the C1 harness connector at the engine control module.
9. Ignition ON, test for 9-11 volts between the vehicle speed signal circuit and ground.

⇒	If less than 9 volts, test the vehicle speed signal circuit for a short to ground or an open/high resistance.

⇒	If greater than 11 volts, test the vehicle speed signal circuit for a short to voltage.

10. 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 detection control module replacement, setup and programming