GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2007 🢒 STS 🢒 Steering 🢒 Steering Wheel and Column 🢒 DTC P0608

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

DTC Descriptors

DTC B0608: Vehicle Speed Output Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Vehicle Speed Signal Circuit

P0608

P0608

1

P0608

1. Speedometer and/or Odometer Inaccurate or Inoperative

Circuit/System Description

The engine control module (ECM) creates the vehicle speed output signal by pulsing the vehicle speed signal circuit to ground at a rate of 4KPPM. The ECM monitors the voltage at the vehicle speed output signal circuit to determine when the voltage is out of the normal operating range. The instrument panel cluster (IPC) receives vehicle speed data from the ECM via the serial data circuit for display in the speedometer. The radio, object detection module and the inside rearview mirror (ISRVM) receive vehicle speed data via a discreet vehicle speed signal circuit from the ECM. The radio, object detection module and the ISRVM use the 4KPPM vehicle speed signal from the ECM to determine vehicle speed.

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.
    • The ECM receives a clear code command from the scan tool.

Reference Information

Schematic Reference

    •  Instrument Cluster Schematics
    •  Radio/Navigation System Schematics
    •  Object Detection Schematics
    •  Inside Rearview Mirror Schematics
    •  Engine Controls Schematics for the 4.6L engine
    •  Engine Controls Schematics for the 4.4L engine
    •  Engine Controls Schematics for the 3.6L engine

Connector End View Reference

    •  Displays and Gages Connector End Views
    •  Entertainment/Communication Connector End Views
    •  Object Detection Connector End Views
    •  Mirror Connector End Views
    •  Engine Control Module Connector End Views for the 4.6L engine
    •  Engine Control Module Connector End Views for the 4.4L engine
    •  Engine Control Module Connector End Views for the 3.6L engine

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Verification

Start the engine with the scan tool installed, the vehicle drive wheels raised and the transmission placed in drive or the first gear. Refer to Lifting and Jacking the Vehicle . Verify that the speedometer display does not match the scan tool Vehicle Speed parameter in the ECM Engine Data List.

Circuit/System Testing

Important: The drive wheels of the vehicle must be raised and the transmission must be placed in drive or first gear. Refer to Lifting and Jacking the Vehicle .

  1. Ignition OFF, disconnect the harness connector at the rear object sensor control module.
  2. Start the engine, with the drive wheels raised and the vehicle placed in drive or the first gear. Verify that the speedometer value does not match the scan tool Vehicle Speed parameter in the ECM Engine Data List.
    3. ⇒If the speedometer matches the scan tool Vehicle Speed parameter, test the vehicle speed signal circuit for a short to voltage, a short to ground or an open/high resistance. If circuit tests normal, replace the rear object sensor control module.
  3. Ignition OFF, disconnect the harness connector at the inside rearview mirror (ISRVM).
  4. Start the engine, with the drive wheels raised and the vehicle placed in drive or the first gear. Verify that the speedometer value does not match the scan tool Vehicle Speed parameter in the ECM Engine Data List.
    5. ⇒If the speedometer matches the scan tool Vehicle Speed parameter, test the vehicle speed signal circuit for a short to voltage, a short to ground or an open/high resistance. If circuit tests normal, replace the ISRVM.
  5. Ignition OFF disconnect the C1 (4.6L and 4.4L) or C2 (3.6L) harness connector at the engine control module.
  6. Ignition ON, test for 9-11 volts between the vehicle speed signal circuit and ground.
    7. ⇒If less than 9 volts, test the vehicle speed signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the radio.
    ⇒If greater than 11 volts, test the vehicle speed signal circuit for a short to voltage. If the circuit tests normal, replace the radio.
  7. If all circuits test normal, test or replace the ECM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for the ECM, radio, object detection module and ISRVM replacement, setup and programming