Vehicle Speed Output Circuit Diagnosis

Circuit Description
Various components apply a voltage to the Vehicle Speed Output circuit. The PCM creates the Vehicle Speed Output signal by rapidly grounding this circuit via an internal switch called a driver. The driver operates at the same rate as the VSS signal input. The various components recognize the voltage being pulled to ground as an indication of vehicle speed.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

For an intermittent, refer to Symptoms. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. Further circuit diagnosis may require I/P removal. Test the circuit from the PCM to the tachometer for being open, shorted to ground or, voltage.
3. This step is testing for the proper signal voltage.
4. This step is testing for an open circuit between the IPC and connector C100.
5. This step is testing for a grounded circuit between the IPC and connector C100.
6. This step is testing for an open circuit between the PCM and connector C100.
7. This step is testing for a grounded circuit between the PCM and connector C100.