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.
Engine Light Check
"CHECK ENGINE" light is used by ECM to indicate and diagnose a fault in electronic control system. Power is supplied to the light from ECM fuse and ground is supplied through the ECM. Light is normally "ON" with key "ON," and should turn "OFF" when engine RPM exceeds 400 RPM.
- This step checks for power to ECM. Normal reading is battery voltage.
- This step checks for an open circuit to ECM. Normal reading at ECM terminal "E" should be battery voltage.
- This step checks for good ECM ground. If there is a poor connection to ground, voltage at terminal "K" will be more than 1 volt. The poorer the ground, the higher the voltage.
NO RELATED
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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.