GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra - 2WD 🢒 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) monitors the MIL control circuit for conditions that are incorrect for the commanded states of the MIL. For example, a failure condition exists if the ECM detects low voltage when the MIL is commanded OFF, or high voltage when the MIL is commanded ON.

Diagnostic Aids

If the condition is intermittent, move the related harnesses and connectors with the engine operating. Inspect the connector terminals and any inline harness connectors for a condition that may result in excessive resistance. Refer to Testing for Intermittent Conditions and Poor Connections.

Reference Information

Schematic Reference

    •  Engine Controls Schematics
    •  Instrument Cluster Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views
    •  Engine Controls Component Views
    •  Displays and Gages Connector End Views
    •  Displays and Gages Component 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

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification
  1. Ignition ON, command the MIL ON and OFF with a scan tool. The MIL should turn ON and OFF as commanded.
  2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame Records data.

Circuit/System Testing
  1. Ignition ON, verify that the instrument panel cluster (IPC) warning indicators are illuminated.
    2. ⇒If the IPC warning indicators are not illuminated, test the IPC 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.
  2. Ignition OFF, disconnect the ECM X2 harness connector. Ignition ON, the MIL should not illuminate.
    3. ⇒If the MIL is illuminated, test the MIL control circuit terminal X2-30 for a short to ground. If the circuit tests normal, replace the IPC.
  3. Ignition ON, connect a 3A fused jumper wire between the MIL control circuit terminal X2-30 and ground. The MIL should illuminate.
    4. ⇒If the MIL does not illuminate, test the MIL control circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the IPC/bulb.
  4. If all circuits test normal, replace the ECM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Instrument Cluster Replacement
    •  Control Module References for ECM and ICM replacement, setup, and programming