A toothed wheel mounted on the output shaft of the transmission generates an AC voltage pulse as it moves past the Vehicle Speed Sensor (VSS). The VSS contains a permanent magnet surrounded by a coil of wire, which produces a magnetic field. The toothed wheel interrupts the magnetic field that generates an AC voltage pulse. As the vehicle speed increases the AC voltage pulse rate also increases.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Engine Control Module Connector End Views

Electrical Information Reference

Scan Tool Reference

Engine Control Module Scan Tool Information

1. Ignition OFF, raise the drive wheels.
2. Engine idling in gear, observe the scan tool VSS parameter and the Speedometer. Both should display a vehicle speed.

1. Ignition OFF, disconnect the harness connector at the VSS.
2. Test for less than 5 ohms between the low reference circuit terminal A and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for B+ between the ignition voltage circuit terminal C and ground.

⇒	If less than the specified range, repair the ignition voltage circuit for a short to ground, or an open/high resistance.

4. Test for 4.8-5.2 volts between the signal circuit terminal B and ground.

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

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

5. If all circuits test normal, test the VSS.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.