GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 XLR 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 DTC P0608

Circuit Description

The engine control module (ECM) creates the vehicle speed output signal by pulsing the circuit to ground. The ECM monitors the voltage on the vehicle speed output circuit. If the ECM 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 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 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

1

Did you perform the Vehicle Diagnostic System Check?

Go to Step 2

Go to Symptoms - Instrument Panel, Gages and Console

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.
  5. With the scan tool, observe the Vehicle Speed parameter in the ECM Engine Data 2 data list.

Does the Vehicle Speed parameter match the speedometer display?

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

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM) connector C1.
  3. Install one lead of the J 33431-C to the vehicle speed signal circuit at the ECM harness connector, and the other lead to a good ground.
  4. Turn ON the ignition, with the engine OFF.
  5. Set the J 33431-C to generate a speedometer signal.

Does the vehicle speedometer indicate approximately 55 MPH?

Go to Step 5

Go to Step 4

4

Test the vehicle speed signal circuit for the following:

    • An open
    • A short to voltage
    • A short to ground

Refer to Circuit Testing and to 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 harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and to 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 to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 8

7

Important: Program the replacement ECM.

Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls.

Did you complete the replacement?

Go to Step 9

--

8

Important:  Perform the set up procedure for the replacement IPC.

Replace the IPC. Refer to Instrument Cluster Replacement .

Did you complete the replacement?

Go to Step 9

--

9
  1. Use the scan tool in order to clear the DTCs.
  2. Operate vehicle within the Conditions for Running this DTC.

Does the DTC reset?

Go to Step 2

System OK