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.
Computerized Engine Controls: Notes
Engine control system uses an Electronic Control Module (ECM), also known as Electronic Control Unit (ECU). Programs for calculation of fuel injection duration, ignition timing and idle speed are stored inside the ECM and are matched with various engine condition data relayed by input sensors. See Fig 1-4. The ECM uses these data signals from various sensors in the vehicle and makes calculations with stored programs to determine fuel injection duration, ignition timing and idle speed, and outputs control signals to respective actuators that control engine operation.
Engine ECM and transmission ECM are integrated into one ECM. The ECM is also equipped with a self-diagnostic function. Trouble codes are set by malfunction of engine sensors or circuits, and are stored in the ECM memory. A Malfunction Indicator Light (MIL), also known as CHECK ENGINE light, on the instrument panel will turn on if a trouble code is stored.
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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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