GM Service Manual Online
For 1990-2009 cars only

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step tests for the proper vehicle speed signal from the PCM.

Step

Action

Value(s)

Yes

No

Schematic Reference: Instrument Cluster Schematics

1

Did you perform the Instrument Cluster Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - Instrument Cluster

2

  1. Install a scan tool.
  2. Raise the vehicle's 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 PCM Engine Data list.

Does the Vehicle Speed parameter match the speedometer display?

--

Go to Step 3

Go to Step 4

3

Does the odometer operate properly?

--

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

Go to Step 8

4

  1. Turn the ignition OFF.
  2. Disconnect connector C1 at the PCM.
  3. Turn the ignition ON with the engine OFF.
  4. Measure the voltage from the vehicle speed signal circuit to a good ground.

Does the voltage measure greater than the specified value?

9.0 V

Go to Step 6

Go to Step 5

5

Test the vehicle speed signal circuit for an open, for a high resistance, or for 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 11

Go to Step 7

6

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

Did you find and correct the condition?

--

Go to Step 11

Go to Step 9

7

Inspect for poor connections at the harness connector of the 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 11

Go to Step 8

8

Inspect for poor connections at the harness connector of the PCM. 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 11

Go to Step 10

9

Replace the IPC. Refer to Instrument Cluster Replacement .

Did you complete the replacement?

--

Go to Step 11

--

10

Important: Program the replacement PCM.

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls.

Did you complete the replacement?

--

Go to Step 11

--

11

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2