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.
Circuit Description
The ignition switch provides circuit power and the ECM provides the circuit ground that illuminates the MIL. MIL operation is checked visually:
It should be illuminated when the ignition is first turned on. If the MIL is off all of the time or on all of the time, use the procedure below to troubleshoot it. The MIL is used to indicate the ECM's detection of vehicle malfunction. Follow this procedure using the hand-held tester or an OBD II scan tool to determine the cause of the problem and to check the MIL.
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.