Sierra Classic 2500 4WD V8-6.0L (2007)
Malfunction Indicator Lamp: Testing and Inspection
Malfunction Indicator Lamp (MIL) Diagnosis
MALFUNCTION INDICATOR LAMP (MIL) DIAGNOSIS
DIAGNOSTIC INSTRUCTIONS
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Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection/Initial Inspection and
Diagnostic Overview/Diagnostic System Check - Vehicle
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Review Strategy Based Diagnosis for an overview of the diagnostic approach.
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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.
Ignition voltage is supplied to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL
control circuit.
CIRCUIT/SYSTEM VERIFICATION
The MIL should turn ON and OFF when commanded with a scan tool.
CIRCUIT/SYSTEM TESTING
1. Ignition OFF, disconnect the harness connector at the instrument panel cluster (IPC).
2. Ignition ON, verify that a test lamp illuminates between the ignition circuit and ground.
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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.
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If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.
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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. See: Powertrain Management/Computers and Control
Systems/Testing and Inspection/Diagnostic Trouble Code Tests and Associated Procedures/Verification Tests and Procedures
Control Module References for ECM and IPC replacement, setup, and programming. See: Testing and Inspection/Programming and Relearning
