Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using the diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC P0608: Vehicle Speed Output CircuitDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Vehicle Speed Signal | P0608 | P0608 | P0608 | -- |
Speedometer Inaccurate or Inoperative | ||||
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
Connector End View Reference
Description and Operation
Instrument Cluster Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
- 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.
- Ignition ON, set the signal generator to generate a speedometer signal. Verify that the vehicle speedometer indicates a reading.
- If all circuits test normal, test or replace the ECM.
| ⇒ | 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). |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for the ECM and IPC replacement, setup, and programming.
