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.
Fail-Safe Function
When a malfunction occurs within the engine control system, the PCM maintains control over the fuel injection system, idle speed control system, etc. PCM controls these systems by using calculated values and/or backup programs stored within the PCM. This function is called the fail-safe function. With the fail-safe function, a certain level of engine performance is available even when a malfunction occurs. The fail-safe function prevents a complete loss of engine performance. The systems covered by the fail-safe function are:
- Mass Air Flow (MAF) sensor.
- Intake Air Temperature (IAT) sensor.
- Throttle Position (TP) sensor.
- HO2S heater circuits.
- Knock Sensor (KS) system.
- Central Processor Unit (CPU) in the PCM.
- Fuel cut-off for ignition system failures.
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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.