P0656

DTC P0654

Diagnostic Instructions

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



DTC Descriptor
DTC B0654
- Engine Speed Output Circuit




Diagnostic Fault Information






Circuit/System Description

The engine control module (ECM) creates the engine speed signal by pulsing the engine speed signal circuit to ground at a rate of 2 pulses per engine revolution. The IPC converts the 2 pulses per engine revolution signal to a tachometer position indicating the engine speed. The engine speed is sent to the instrument panel cluster (IPC) over a discreet circuit from the ECM. The tachometer signal is pulled up to B+ in the instrument panel cluster (IPC). The ECM monitors the voltage at the engine speed signal circuit to determine when the voltage is out of the normal operating range.


Conditions for Running the DTC

* The engine speed is more than 400 RPM.
* The ignition voltage is between 9-18 volts.



Conditions for Setting the DTC

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



Action Taken When the DTC Sets

The ECM records the operating conditions at the time the diagnostic fails. The ECM displays the failure information in the Failure Records on the scan tool.


Conditions for Clearing the DTC

* The DTC becomes history when the conditions for setting the DTC are no longer present.
* The history DTC clears after 40 malfunction-free warm-up cycles.



Reference Information
Schematic Reference

Instrument Cluster Schematics (Instrument Cluster Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Instrument Cluster Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning)


Circuit/System Verification

Start the engine with the scan tool installed. Verify that the tachometer display matches the scan tool Engine Speed parameter in the ECM Engine Data List.


Circuit/System Testing

1. Ignition OFF, disconnect the X1 harness connector at the engine control module.
2. Ignition ON, test for 9-11 volts between the engine speed signal circuit terminal 25 and ground.

• If less than 9 volts, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the IPC.


• If greater than 11 volts, test the signal circuit for a short to voltage. If the circuit tests normal, replace the IPC.

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



Repair Instructions

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


Control Module References (Programming and Relearning) for the ECM or IPC replacement, setup and programming