Circuit/System Testing

Install a scan tool.
Raise the vehicles drive wheels.
Start the engine.
Place the transmission into drive.
With the scan tool, observe the Vehicle Speed Sensor (VSS) parameter in the ECM Engine Data list.
- If the vehicle speed sensor parameter matches the speedometer display, check for a poor connection at the harness connector of the ECM/PCM.
Turn OFF the ignition.
Disconnect the ECM/PCM connector C000.
With the ignition ON, measure the voltage from the vehicle speed signal circuit to a good ground.
- If the voltage measured is more than 9 V, test the vehicle speed signal circuit for a short to battery voltage.

If the voltage measured is less than 9 V, test the vehicle speed signal circuit for an open, a high resistance or for a short to ground.