Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Malfunction Indicator Lamp (MIL)
The Malfunction Indicator Lamp (MIL) is required by On-Board Diagnostics (OBD II) to illuminate under a strict set of guidelines.
Basically, the MIL is turned ON when the Engine Control Module (ECM) detects a DTC that will impact the vehicle emissions.
The MIL is under the control of the Diagnostic Executive. The MIL will be turned ON if an emissions-related diagnostic test indicates a malfunction has occurred. It will stay on until the system or component passes the same test for three consecutive trips with no emissions related faults.
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.