GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Blazer - 4WD 🢒 Restraints 🢒 SIR 🢒 DTC P0608

Circuit Description

The powertrain control module (PCM) creates the vehicle speed output signal by pulsing the circuit to ground. The PCM pulses the circuit at the same rate as the vehicle speed signal input. The PCM monitors the voltage on the vehicle speed signal circuit. If the PCM determines the voltage is out of the normal operating range, a DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0608 Vehicle Speed Output Circuit

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 PCM detects that the voltage of the vehicle speed signal circuit is out of the normal operating range.
    • The condition must be present for a minimum of 5 seconds.

Action Taken When the DTC Sets
    • The PCM stores the DTC information in memory when the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The 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 PCM receives the clear code command from the scan tool.

Step

Action

Yes

No

Schematic Reference: Instrument Cluster Schematics

Connector End View Reference: Powertrain Control Module Connector End Views in Engine Controls - 4.3L, or Instrument Panel, Gages, and Console Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Install a scan tool.
  2. Raise the vehicles drive wheels. Refer to Lifting and Jacking the Vehicle in General Information.
  3. Start the engine.
  4. Place the transmission into drive for an automatic transmission and third gear for a manual transmission.
  5. With the scan tool, observe the Vehicle Speed Sensor parameter in the powertrain control module (PCM) Engine Data 1 data list.

Does the Vehicle Speed Sensor parameter match the speedometer display?

Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Disconnect the PCM connector C2.
  3. Install the Signal Generator and Instrument Panel Tester J 33431-C lead to the vehicle speed signal circuit at the PCM harness connector, and the other lead to a good ground.
  4. Turn the ignition ON, with the engine OFF.
  5. Set the Signal Generator and Instrument Panel Tester J 33431-C to generate a speedometer signal.

Does the vehicle speedometer indicate approximately 89 km/h (55 mph)?

Go to Step 5

Go to Step 4

4

Test the vehicle speed signal circuit for an open, for a short to voltage, or for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 6

5

Inspect for poor connections at the PCM connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 7

6

Inspect for poor connections at the harness connector of the instrument panel cluster (IPC) . Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 8

7

Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 9

--

8

Replace the IPC. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 9

--

9
  1. Use the scan tool in order to clear the DTC.
  2. Operate vehicle within the conditions for running this DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK