GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Malfunction Indicator Lamp (MIL) Diagnosis

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The malfunction indicator lamp (MIL) is located on the instrument panel cluster (IPC). The MIL informs the driver that an emission system fault has occurred and that the engine control system requires service. The engine control module (ECM) performs a self test for the MIL lamp and its circuitry by commanding the MIL ON and OFF every time the engine is started. The ECM monitors the MIL control circuit for conditions that are incorrect for the commanded states of the MIL.

Reference Information

Schematic Reference

    •  Engine Controls Schematics
    •  Instrument Cluster Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Ignition ON, command the MIL ON and OFF with a scan tool. Observe the MIL, it should turn ON and OFF with each command.
  2. Engine running, observe the DTC information with a scan tool. DTC P0650 should not set.
  3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame Records data.

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connector at the IPC.
  2. Ignition ON, verify that a test lamp illuminates between the ignition circuit and ground.
    3. ⇒If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, replace the IPC.
  3. Connect a test lamp between the control circuit and the ignition circuit.
  4. Command the MIL ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    5. ⇒If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.
    ⇒If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
  5. If all circuits test normal, replace the IPC.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM and ICM replacement, setup, and programming