GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 Speedometer and/or Odometer Inaccurate or Inoperative

Test Description

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

  1. This step tests for the proper vehicle speed signal from the powertrain control module (PCM).

Step

Action

Value(s)

Yes

No

Schematic Reference: Instrument Cluster Schematics

Connector End View Reference: Master Electrical Component List in Wiring Systems

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 powertrain control module (PCM) connector C2 (L18, LLY and LB7) or C3 (LG4).
  3. Install one lead of the J 33431-C 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 J 33431-C to generate a speedometer signal.

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

--

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 PCM connector C2 (L18, LLY and LB7) or C3 (LG4).
  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?

9.0 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 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 11

Go to Step 9

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

Important: Program the replacement IPC.

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:

    •  Engine Control Module Replacement in Engine Controls - 6.6L (LB7).
    •  Engine Control Module Replacement in Engine Controls - 6.6L (LLY).
    •  Engine Control Module Replacement/Restore Fuel Rate Data in Engine Controls - 7.8L.
    •  Powertrain Control Module Replacement in Engine Controls - 8.1L.

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