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 Light (Mil)
Engine Control Module (ECM) is equipped with self-diagnostic system. By analyzing various input signals, ECM detects system malfunctions related to various operating parameters. When malfunction occurs, ECM will inform driver by turning on Malfunction Indicator Light (MIL) on instrument panel. If self-diagnostic system detects a fault, it stores a trouble code in ECM memory and grounds MIL circuit, which causes MIL to come on. For more information, see appropriate SELF-DIAGNOSTICS article.
Diagnostic Trouble Codes (DTC) may be set by malfunction of various engine sensors, switches or circuits. DTC is stored in ECM memory. When DTC is stored, MIL on instrument panel will come on. DTC can be retrieved for system diagnosis. For additional information on self-diagnostic system, see appropriate SELF-DIAGNOSTICS article.
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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.