P0654

CIRCUIT DESCRIPTION
The PCM creates the engine speed output signal by pulsing the circuit to ground at a predetermined hertz rate. The PCM pulses the circuit at the same rate as the engine speed signal input. The PCM monitors the voltage on the engine speed output circuit. If the PCM determines the voltage is out of the normal operating range, a DTC sets.

CONDITIONS FOR RUNNING THE DTC
^ The engine speed is greater than 400 RPM.
^ The ignition voltage is greater than 6 volts, but less than 18 volts.

CONDITIONS FOR SETTING THE DTC
^ The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match.
^ All of the above conditions exist for a minimum of 5.0 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM stores the DTC information into memory when the diagnostic runs and fails.
^ The malfunction indicator lamp (MIL) will not illuminate.
^ The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ A last test failed (current DTC) clears when the diagnostic runs and does not fail.
^ A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
^ Use a scan tool in order to clear the MIL/DTC.

DIAGNOSTIC AIDS

IMPORTANT: Remove any debris from the PCM module 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 contaminate intrusion into the PCM.

For an intermittent, refer to Testing for Intermittent and Poor Connections in Diagnostic Aids.

TEST DESCRIPTION

Steps 1-3:

Steps 4-9:

The numbers below refer to the step numbers on the diagnostic table.
3. Further circuit diagnosis may require IPC removal. Test the circuit from the PCM to the tachometer for being open, shorted to ground or, voltage. If you can not find any trouble, follow the appropriate IPC diagnostic procedure.