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 🢒 Reduced Engine Power Lamp Control 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

The PCM will turn the REDUCED ENGINE POWER lamp ON when ignition positive voltage is supplied to the REDUCED ENGINE POWER lamp. The PCM controls the lamp by grounding the control circuit with an internal switch called a driver.

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

    • The ignition switch is turned to the ON position.
    • The PCM is in the REDUCED ENGINE POWER mode.

The PCM will turn the REDUCED ENGINE POWER 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 not in the REDUCED ENGINE POWER mode

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 for the following conditions:

    • A terminal that is backed out of the connector.
    • A connector that is improperly mated.
    • Connector locks that are broken.
    • Terminals that are deformed or damaged.
    • Poor terminal to wire connections.
    • A wiring harness that is damaged.

Test Description

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

  1. Review the scan tool DTC information in order to determine the malfunction causing the PCM to be in the reduced power mode.

    2.

  2. 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 REDUCED ENGINE POWER lamp.

Did the lamp illuminate?

10 seconds

Go to Step 3

Go to Step 6

3

Does the scan tool indicate that the PCM is in the Reduced Engine Power mode?

--

System OK

Go to Step 4

4

Did the REDUCED ENGINE POWER lamp turn OFF after the specified value?

5 seconds

System OK

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector containing the REDUCED ENGINE POWER 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 REDUCED ENGINE POWER lamp control circuit

Did you find and repair a problem?

--

Go to Step 2

Go to Step 9

6
  1. Disconnect the PCM connector containing the REDUCED ENGINE POWER lamp control circuit.
  2. Connect a fused jumper to battery ground and probe the REDUCED ENGINE POWER lamp control circuit at the PCM connector.
  3. Turn the ignition switch to the ON position.

Is the lamp ON?

--

Go to Step  7

Go to Step 8

7

Inspect the PCM connector for the following conditions:

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

Did you find and repair a problem?

--

Go to Step 2

Go to Step 9

8

Check for the following conditions and repair as necessary:

    • Faulty bulb
    • Open ignition feed to the bulb
    • Open lamp control circuit between the lamp and the PCM

Is the action complete?

--

Go to Step 2

--

9

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

Replace the PCM.

Is the action complete?

--

Go to Step 2

--