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.

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

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 harness connector at the rear object sensor control module.
2. With the drive wheels raised start the engine and place the vehicle transmission 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 the circuit tests normal, replace the rear object sensor control module.

3. Ignition OFF, disconnect the harness connector at the inside rearview mirror (ISRVM).
4. With the drive wheels raised start the engine and place the vehicle transmission 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 6 for a short to voltage, a short to ground or an open/high resistance. If circuit tests normal, replace the ISRVM.

5. Ignition OFF disconnect the X1 (LH2 and LC3) or X2 (LY7) harness connector at the engine control module.
6. Ignition ON, test for 9-11 volts between the vehicle speed signal circuit terminal 39 (LH2 and LC3) or terminal 22 (LY7) 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 radio.

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

7. 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, radio, rear object detection module and ISRVM replacement, setup and programming