GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 ENGINE OVERSPEED Lamp Circuit Diagnosis

Refer to

Cell 20: Driver Information Center, Engine Controls


Object Number: 330351 Size: FS
Engine Controls Components
Cell 20: IP Cluster, Transmission Controls, Multifuction Alarm Module
Handling ESD Sensitive Parts Notice

Circuit Description

Ignition positive voltage is supplied to the ENGINE OVERSPEED lamp when the ignition switch is turned to the ON position. The PCM controls the lamp by grounding the control circuit with an internal switch called a driver.

The PCM will turn the ENGINE OVERSPEED lamp ON when any of the following conditions exist:

    • The ignition switch is turned to the ON position.
    • The PCM is detecting an engine speed greater than the calibrated maximum engine speed limit.

The PCM will turn the ENGINE OVERSPEED lamp OFF when any of the following conditions exist:

    • The ignition switch has been turned to the ON position for at least 5 seconds
    •  The PCM is detecting an engine speed less than the calibrated maximum engine speed limit.

Diagnostic Aids

An open ignition positive voltage fuse/circuit breaker will cause the entire IP cluster to be inoperative.

Inspect the related circuits and components that are suspected of causing an intermittent problem. Refer to Symptoms .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step will determine if the PCM is controlling the lamp.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Turn the ignition switch to the OFF position for the specified value.
  2. Turn the ignition switch to the ON position and observe the ENGINE OVERSPEED lamp.

Did the lamp illuminate?

10 seconds

Go to Step 3

Go to Step 5

3

Did the ENGINE OVERSPEED lamp turn OFF after the specified value?.

5 seconds

System OK

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector containing the ENGINE OVERSPEED lamp control circuit.
  3. Turn the ignition switch to the ON position.
  4. If the lamp is ON, repair the short to ground at the ENGINE OVERSPEED lamp control circuit

Did you find and repair a problem?

--

Go to Step 2

Go to Step 8

5
  1. Disconnect the PCM connector containing the ENGINE OVERSPEED lamp control circuit.
  2. Connect a fused jumper to battery ground and probe the ENGINE OVERSPEED lamp control circuit at the PCM connector.
  3. Turn the ignition switch to the ON position.

Is the lamp ON?

--

Go to Step  6

Go to Step 7

6

Inspect the PCM connector for the following conditions:

    • Damaged or deformed terminals.
    • Terminals that are improperly positioned.

Refer to Wiring Repairs in Wiring Systems.

Did you find and repair a problem?

--

Go to Step 2

Go to Step 7

7

Check for the following conditions and repair as necessary:

    • Faulty bulb
    • Refer to Wiring Repairs in Wiring Systems.
    • Open lamp control circuit between the lamp and the PCM.

Is the action complete?

--

Go to Step 2

--

8

Important:: Program the replacement PCM. Go to Powertrain Control Module Replacement .

Replace the PCM.

Is the action complete?

--

Go to Step 2

--