GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The 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 output circuit. If the PCM determines the voltage is out of the normal operating range, a DTC sets.

Conditions for Running the DTC

    â€¢ The engine speed is greater than 400 RPM.
    â€¢ The ignition voltage is greater than 6 volts but less than 18 volts.

Conditions for Setting the DTC

    â€¢ The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match.
    â€¢ The condition must be present for a minimum of 5 seconds.

Action Taken When the DTC Sets

    â€¢ The PCM stores the DTC information in memory.
    â€¢ The PCM 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

    â€¢ The history DTC clears after 40 malfunction free warm-up cycles.
    â€¢ The DTC becomes history when the conditions for setting the DTC are no longer present.
    â€¢ The PCM receives the clear code command from the scan tool.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed.

For an intermittent, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Step

Action

Value(s)

Yes

No

Schematic Reference: Instrument Cluster Schematics

Connector End View Reference: Master Electrical Component List

1

Did you perform the Instrument Cluster Diagnostic System Check?

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Go to Step 2

Go to Diagnostic System Check - Instrument Cluster

2

  1. Turn the ignition OFF.
  2. Raise the vehicle 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 or third gear for manual transmission.

Does the vehicle speedometer indicate a vehicle speed?

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Go to Diagnostic Aids

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Disconnect the PCM connector C2.
  3. Turn the ignition ON, with the engine OFF.
  4. Measure the voltage from the vehicle speed signal circuit of the PCM to a good ground.

Does the voltage measure greater than the specified value?

9.5 V

Go to Step 4

Go to Step 6

4

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

Did you find and correct the condition?

--

Go to Step 8

Go to Step 5

5

Inspect for poor connections at the harness connector of the PCM. 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 8

Go to Step 7

6

Repair the short to ground in the vehicle speed signal circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 8

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7

Important: Program the replacement PCM.

Replace the PCM. Refer to the following procedures:

    â€¢  Powertrain Control Module Replacement in Engine Controls - 4.3L
    â€¢  Powertrain Control Module Replacement in Engine Controls - 4.8L, 5.3L and 6.0L
    â€¢  Engine Control Module Replacement in Engine Controls - 6.6L (LB7)
    â€¢  Engine Control Module Replacement in Engine Controls - 6.6L (LLY)
    â€¢  Powertrain Control Module Replacement in Engine Controls - 8.1L

Did you complete the replacement?

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Go to Step 8

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8

  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

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Go to Step 2

System OK