GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2004 🢒 Isuzu MD F-Series 🢒 Driveline/Axle 🢒 Rear Drive Axle 🢒 Speedometer and/or Odometer Inaccurate or Inoperative

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. Turn the ignition OFF.
  2. Disconnect the following engine control module (ECM) connectors:
    3. • C3:w/o CTF
    • C1:CTF
  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 the ignition ON, with the engine OFF.
  5. Set the J 33431-C to generate a speedometer signal.

Does the vehicle speedometer indicate approximately 55 MPH (88.5 km/h)?

--

Go to Step 3

Go to Step 4

3

Does the odometer operate correctly?

--

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

Go to Step 9

4

  1. Turn the ignition OFF.
  2. Disconnect the following ECM connectors:
    3. • C3:w/o CTF
    • C1:CTF
  3. Turn the ignition ON.
  4. Measure the voltage from the vehicle speed signal circuit to a good ground.

Does the voltage measure greater than the specified value?

9 V

Go to Step 6

Go to Step 5

5

Test the vehicle speed signal circuit for an open, for a short to ground or for a high resistance. 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 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 8

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 9

8

Inspect for poor connections at the harness connector of the 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 11

Go to Step 10

9

Important: Program the replacement instrument panel cluster (IPC).

Replace the IPC. Refer to Instrument Cluster Replacement .

Did you complete the replacement?

--

Go to Step 11

--

10

Important: Program the replacement ECM.

Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data in Engine Controls - 7.8L.

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