P0608

DTC P0608

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 P0608
- Vehicle Speed Output Circuit

Diagnostic Fault Information





Circuit Description

The engine control module (ECM) creates the vehicle speed signal by pulsing the vehicle speed signal circuit to ground at a rate of 4KPPM. The instrument panel cluster (IPC) converts the 4KPPM vehicle speed signal to a speedometer position to indicate the vehicle speed. The IPC also receives from the ECM a serial data message indicating the vehicle speed. The IPC uses the serial data vehicle speed information from the ECM for diagnostics purposes. The ECM monitors the voltage on the vehicle speed signal circuit and determines 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 6-18 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 MIL/DTC

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

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 (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 (Programming and Relearning) for scan tool information

Circuit/System Testing

1. Ignition OFF, disconnect the X1 harness connector at the ECM. Install a signal generator and instrument panel tester between the vehicle speed signal circuit terminal 39 and ground.
2. Ignition ON, set the signal generator to generate a speedometer signal. Verify that the vehicle speedometer indicates a reading.

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