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.
Check Engine Light & Malfunction Indicator Light (Mil)
CHECK ENGINE light and MIL are intended to alert driver of certain malfunctions in EEC-IV system.
Light may also be used to retrieve service codes stored in PCM. When hooked up for KOEO SELF-TEST or KOER SELF-TEST, light will display all codes which turn on light during vehicle operation, not just Continuous Memory Codes.
If light comes on during vehicle operation, vehicle should be inspected as soon as possible. It is not necessary to immediately turn off engine. Vehicle can be driven with light on.
If light comes on and then goes off during vehicle operation, code causing light to glow will be stored in PCM memory as a Continuous Memory Code.
Light should come on when ignition is turned on and go out when engine is started. If hard fault codes are not present, PCM turns out light when it receives a Profile Ignition Pick-Up (PIP) signal. If light does not come on, see SYMPTOMS in appropriate TESTS W/O CODES article in ENGINE PERFORMANCE.
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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.