DTC P0608. GMC Truck TopKick C-Series (Conventional) C4/C5 2008

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2008 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0608

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 Circuit

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Vehicle Speed Signal	B0540, P0608	B0540, P0608	B0540, P0608	--

The engine control module (ECM)/powertrain control module (PCM) creates the vehicle speed output signal by pulsing the circuit to ground at a rate of 4K PPM. The ECM/PCM monitors the voltage at the vehicle speed output circuit. If the ECM/PCM determines that the voltage is out of normal operating range, the ECM/PCM sets a DTC.

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/PCM detects that the commanded state of the driver and the actual state of the signal circuit do not match.

•	The condition above must be present for a minimum of 5 seconds.

Action Taken When the DTC Sets

•	The ECM/PCM stores a DTC P0608 in memory when the diagnostic test runs and fails.

•	The malfunction indicator lamp (MIL) will not illuminate.

•	The ECM/PCM records the operating conditions at the time the diagnostic fails. The ECM/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.

Reference Information

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

Ignition OFF, disconnect the harness connector at the ECM/PCM. Install a signal generator and instrument panel tester between ground and the following vehicle speed signal circuit:

•	Terminal 82 (LF8)

•	Terminal 36 LF6)

•	Terminal 50 (L18)

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 an open/high resistance, a short to voltage, or a short to ground. If the circuit tests normal, replace the instrument panel cluster (IPC).

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

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for the ECM/PCM and IPC replacement, setup, and programming