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.
Electronic Control Module (ECM)
ECM controls engine operation based on input signals from various sensors. ECM also controls transmission. If self-diagnostic system detects a fault, it stores a trouble code in the ECM memory, and turns on the Malfunction Indicator Light (MIL), also known as CHECK ENGINE light. For more information, proceed to TESTS W/CODES - EXCEPT OBD-II article in the ENGINE PERFORMANCE section.
If the ECM detects a system fault, it controls fuel injection and ignition timing at predetermined levels as a back-up ("fail-safe") function to make it possible to continue vehicle operation. If engine speed exceeds 6500 RPM, ECM stops fuel injection until engine speed decreases to less than 6500 RPM. This prevents engine overrun.
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.
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