Engine Speed Output Circuit Diagnosis

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
The Instrument Panel Cluster (IPC) supplies a voltage to the engine speed output circuit. The Powertrain Control Module (PCM) creates the engine speed output signal by rapidly grounding this circuit via an internal switch called a driver. The other components on this circuit recognize the voltage being pulled to ground as an indication of engine speed.

The driver supplies the ground for the component being controlled. Each driver has a fault line which the PCM monitors. 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 or 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.
7. This step is testing for an open circuit between the PCM and connector C100.