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"/"Service Engine Soon" - Malfunction Indicator Light (Mil): Notes
The MIL is intended to alert driver of certain malfunctions in the EEC-IV system.
The light may also be used to retrieve service codes stored in ECA. When hooked up for KOEO SELF-TEST or KOER SELF-TEST, light will retrieve all codes, not just Continuous Memory Codes which turn on light during vehicle operation.
If the light comes on during vehicle operation, it should be serviced and inspected as soon as possible. It is not necessary to immediately turn off engine; vehicle can still be driven and does not need to be towed.
If the light comes on then goes off while in operation, the code causing light to illuminate will be stored in ECA 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, ECA turns out the light when it receives a Profile Ignition Pick-Up (PIP) signal. If light never comes on, see SYMPTOMS in the TESTS W/O CODES 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.