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
The Electronic Control Module (ECM) is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction that may affect vehicle emissions is detected during 2 sequential drive cycles, the ECM will illuminate the Malfunction Indicator Light (MIL) on the instrument panel. See Figure . A corresponding Diagnostic Trouble Code (DTC) will be stored in ECM. If a misfire is detected, MIL will illuminate and DTC will be stored in ECM immediately after fault is detected. If misfire is severe enough to cause catalytic converter damaged, MIL will blink. MIL will continuously blink until danger to catalytic converter has passed. To retrieve stored DTC(s), see RETRIEVING DIAGNOSTIC TROUBLE CODES .
DTC will be erased from ECM memory. If battery is disconnected, all DTCs and freeze frame data will be erased from ECM. As a bulb check, Malfunction Indicator Light (MIL) will also illuminate for about 5 seconds when ignition is turned on.
DTCs will be recorded at various operating times and conditions. Some DTCs require operation of sensor or switch for 5 seconds, while other components require operation for 5 minutes or longer at normal operating temperature, vehicle speed, and load. Therefore, when verifying repair, some DTCs may not set in a service bay and may require road testing to duplicate the conditions under which the code will set.
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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.
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