Vehicle Speed Output Circuit Diagnosis

Schematic:

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. The driver supplies the ground for the component being controlled. When the PCM commands a component ON, the voltage of the control circuit should be low (near 0 volts). When the PCM commands the control circuit to a component OFF, the voltage potential of the circuit should be high (near battery voltage).

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 any test that requires probing the PCM or component harness connectors, use the J 35616-A connector test adapter kit. Using this kit prevents any damage to the harness connector terminals. Refer to Using Connector Test Adapters in Diagrams.

Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the condition, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the condition occurred.

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

TEST DESCRIPTION

Diagnostic Chart:

The numbers below refer to the step numbers on the diagnostic table.
3. This step tests for a voltage to the PCM.
5. This step tests for a short to ground.