P0656

DTC P0654

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using the diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC P0654
^ Engine Speed Output Circuit

Diagnostic Fault Information





Circuit Description

The powertrain control module (PCM) creates the engine speed signal by pulsing the circuit to ground. The engine control module (ECM)/PCM monitors the voltage on the engine speed signal circuit. If the ECM/PCM determines that the voltage is not within the normal operating range, the ECM/PCM sets a DTC.

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 ECM/PCM detects that the commanded state of the driver and the actual state of the signal circuit do not match.
* The above condition exists for a minimum of 5 seconds.

Action Taken When the DTC Sets

* The ECM/PCM stores the DTC information in memory when the diagnostic test runs and fails.
* The malfunction indicator lamp (MIL) will not illuminate.
* The ECM/PCM records the operating conditions at the time when the diagnostic test fails. The ECM/PCM stores this information in the Failure Records.

Conditions for Clearing the MIL/DTC

* The DTC becomes history when the conditions for setting the DTC are no longer present.
* A history DTC is cleared after 40 consecutive malfunction-free warm-up cycles.
* The ECM/PCM receives the clear code command from the scan tool.

Reference Information
Schematic Reference

* Instrument Cluster Schematics (Instrument Cluster Schematics)
* Engine Controls Schematics ([1][2]Electrical Diagrams) for the 4.2L engine
* Engine Controls Schematics ([1][2]Electrical Diagrams) for the 4.8L, 5.3L, 6.0L, 6.2L or 7.0L engines

Connector End View Reference

Component Connector End Views (Component Connector End Views)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Control Module References) for scan tool information

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector X1 at the ECM/PCM. Install a signal generator and instrument panel tester between the following engine speed signal circuit and ground:

* Terminal 31 (4.2L)
* Terminal 25 (5.3L/6.0L)

2. Ignition ON, set the signal generator to generate a tachometer signal. Verify that the tachometer indicates a RPM reading.

• If no RPM reading is present, test the signal circuit for an open/high resistance, a short to voltage, or a short to ground. If the circuit tests normal, replace the instrument panel cluster (IPC).

3. If all circuits test normal, test or replace the ECM/PCM.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

Control Module References (Control Module References) for the ECM/PCM and IPC replacement, setup, and programming