GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2006 🢒 Optra - Mexico 🢒 Engine 🢒 Engine Controls - 1.8L (L79) 🢒 Malfunction Indicator Lamp (MIL) Inoperative

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 provide an overview of each diagnostic category.

Circuit/System Description

Ignition 1 voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.

MIL Operation

The MIL is located on the instrument panel (I/P).

MIL Function
    • The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible.
    • The MIL illuminates during a bulb test and a system test.
    • A DTC will be stored if a MIL is requested by the diagnostic.

MIL Illumination
    • The MIL will illuminate with the ignition switch ON and the engine not running.
    • The MIL will turn OFF when the engine is started.
    • The MIL will remain ON if the self-diagnostic system has detected a malfunction.
    • The MIL may turn OFF if the malfunction is no longer present.
    • If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated as long as the ignition switch is ON.
    • If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

Electrical Information Reference

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

Scan Tool Reference

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

Circuit/System Verification
  1. Turn ON the ignition, command the MIL ON and OFF with a scan tool. The MIL should turn ON and OFF when commanded.
  2. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the FreezeFrame/Failure Records List.

Circuit/System Testing
  1. If any other indicators are inoperative, refer to Symptoms - Instrument Panel, Gages and Console
  2. Ignition OFF, disconnect the ECM harness connector.
  3. Ignition ON, connect a 3-amp fused jumper wire between the MIL control circuit and ground. The MIL should illuminate.
    4. ⇒If the MIL does not illuminate, test the MIL control circuit for a short to ground, or an open/high resistance. If the circuit test normal, replace the IPC/bulb.
    ⇒If the fuse opens, repair the MIL control circuit for a short to voltage.
    ⇒If the MIL illuminates, inspect for a poor connection or replace the control module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Instrument Panel Assembly Replacement
    •  Clock Replacement
    •  Control Module References for engine control module replacement, setup, and programming.