DTC P0608. Chevrolet TrailBlazer

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2007 🢒 TrailBlazer - 2WD 🢒 Driver Information and Entertainment 🢒 Displays and Gages 🢒 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 Circuit	P0608	P0608	P0608	--

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

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/PCM 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/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 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.

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

Reference Information

Schematic Reference

•	Instrument Cluster Schematics

•	Engine Controls Schematics for the 4.2L engine

•	Engine Controls Schematics for the 5.3L engine

•	Engine Controls Schematics for the 6.0L engine

Connector End View Reference

•	Displays and Gages Connector End Views

•	Powertrain Control Module Connector End Views

•	Engine Control Module Connector End Views for the 5.3L engine

•	Engine Control Module Connector End Views for the 6.0L engine

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Scan Tool Reference

Scan Tool Data List

Circuit/System Testing

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