Circuit Description
The powertrain control module (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.
The PCM supplies a voltage to the engine speed output circuit. The 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 PCM 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). If the fault detection circuit senses a voltage other than what is expected, the fault line status changes, causing DTC P0654 to set.
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 Conditions and Poor Connections in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Instrument Cluster Schematics Connector End View Reference: Engine Controls Connector End Views and Powertrain Control Module Connector End Views | ||||
1 | Did you perform the instrument panel cluster (IPC) Diagnostic System Check? | -- | Go to Step 2 | |
2 | With the engine running, does the vehicles tachometer indicate engine RPM? | -- | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
Does the tachometer indicate a RPM? | -- | Go to Step 5 | Go to Step 4 | |
4 | Test the engine speed signal circuit for an open, high resistance, or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 |
5 | Inspect for poor connections at the PCM connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 6 |
6 | Inspect for poor connections at the harness connector of the IPC. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 |
7 |
Important: Program the replacement PCM. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls. Did you complete the replacement? | -- | Go to Step 9 | -- |
8 | Replace the IPC. Refer to Instrument Cluster Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- |
9 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
