P0608

DTC P0608

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* 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 00
- Vehicle Speed Output Circuit

Circuit/System Description

The vehicle speed signal circuit is an input to the throttle actuator control (TAC) module from the powertrain control module (PCM) / engine control module (ECM). The PCM (3.8L) / ECM (5.3L) provides a constant voltage signal on the vehicle speed signal circuit. The PCM creates the vehicle speed signal by internally pulsing the vehicle speed signal to ground. The TAC module uses the vehicle speed signal from the PCM/ECM, in order to determine the vehicle speed. The TAC module then sends a universal asynchronous receiver transmitter (UART) serial data message to the PCM/ECM indicating the vehicle speed that the TAC module has detected.

Conditions for Running the DTC

* The vehicle is in Drive or Reverse.
* The vehicle speed is greater than 8 km/h (5 mph).
* There are no VSS DTCs present in the PCM.
* The ignition voltage is between 9-16 volts.

Conditions for Setting the DTC

* The PCM/ECM sends a 8 km/h (5 mph) signal on the vehicle speed signal circuit to the TAC module. The TAC module sends a UART serial data message to the PCM/ECM indicating that the vehicle speed is 0 km/h (0 mph).
* The condition must be present for greater than 4 seconds.

Action Taken When the DTC Sets

* The cruise control system is disabled.
* The PCM/ECM stores a DTC P0608 in memory.
* The PCM/ECM records the operating conditions at the time the DTC sets. The PCM displays the failure information in the Failure Records on the scan tool.

Conditions for Clearing the 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.
* The PCM/ECM receives the clear code command from the scan tool.

Diagnostic Aids

* If any additional powertrain DTCs are stored, refer to Diagnostic Trouble Code (DTC) List - Vehicle. Diagnostic Trouble Code Descriptions
* For intermittent diagnosis, Refer to Testing for Intermittent Conditions and Poor Connections in Diagnostic Aids. Component Tests and General Diagnostics

Circuit/System Verification

1. Ignition OFF, install a scan tool and raise the vehicle drive wheels. Refer to Vehicle Lifting.
2. Engine ON, transmission in Drive, verify the scan tool Vehicle Speed Sensor parameter reads any vehicle speed.

• If the scan tool parameter does not read any vehicle speed and DTC P0502 or P0503 are current in the PCM/ECM, go to Diagnostic Aids. If those codes are not current, replace the PCM/ECM.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the throttle actuator control (TAC) module.
2. Ignition ON, test for 8.5 V between the vehicle speed signal terminal 4 and ground.

• If less than the specified value, test the vehicle speed signal circuit for a short to ground. If the circuit tests normal, replace the PCM/ECM.

• If greater than the specified value, test the vehicle speed signal circuit for a short to voltage. If the circuit tests normal, replace the TAC module.

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

Repair Instructions

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

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