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.
Self-Diagnostic Function: Notes
The Powertrain Control Module (PCM) diagnoses any troubles which may occur in the engine control system when the ignition switch is in the RUN position with the engine running. The PCM indicates a malfunction by illuminating the Malfunction Indicator Lamp (MIL) when a fault occurs in any of the following systems:
- Heated Oxygen Sensor 1 (HO2S 1).
- Heated Oxygen Sensor 2 (HO2S 2).
- Engine Coolant Temperature (ECT) sensor.
- Throttle Position (TP) sensor (including the CTP switch).
- Vehicle Speed Sensor (VSS).
- Intake Air Temperature (IAT) sensor.
- Mass Air Flow (MAF) sensor.
- Camshaft Position (CMP) sensor.
- Crankshaft Position (CKP) sensor.
- Knock Sensor (KS) system.
- Evaporative Emission (EVAP) control system.
- Idle Air Control (IAC) system.
- CMP actuator solenoid system.
- Rocker arm oil control system.
- Misfire detection.
- Fuel-trim.
- Catalyst monitor.
- Central Processing Unit (CPU) of the PCM.
When PCM detects a malfunction in one of the above areas, the PCM will illuminate or flash the MIL in order to notify the driver of the occurrence of a fault. PCM will store a DTC when PCM illuminates the MIL. PCM will turn OFF the MIL after 3 consecutive ignition cycles without the malfunction occurring. The DTC will remain stored in the PCM memory after the MIL is OFF.
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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.