Common Causes:
* Oxygen Sensor (O2 Sensor) Malfunction: This is a very frequent culprit. O2 sensors measure the oxygen in the exhaust to help the engine computer adjust the air/fuel mixture. A faulty sensor can lead to poor fuel economy, rough idling, and emissions problems.
* Mass Airflow Sensor (MAF) Problem: The MAF sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause a lean or rich fuel mixture, affecting performance and potentially damaging the catalytic converter.
* Catalytic Converter Issues: These are expensive to replace. A failing catalytic converter can be caused by other problems (like a faulty O2 sensor or excessive oil consumption).
* Ignition System Problems: Issues with spark plugs, ignition coils, or wires can cause misfires, leading to the check engine light.
* Transmission Problems: While less common to trigger *just* the check engine light, transmission issues can sometimes do so. Slipping, harsh shifting, or other transmission problems might also be accompanied by other symptoms.
* PCV Valve (Positive Crankcase Ventilation) Failure: A clogged PCV valve can cause excessive crankcase pressure, leading to oil leaks and affecting engine performance.
* Throttle Position Sensor (TPS) Malfunction: The TPS tells the computer the throttle position. A faulty TPS can cause poor idle, hesitation, and rough running.
Less Common but Possible Causes:
* Exhaust Leaks: Leaks in the exhaust system can affect the O2 sensor readings.
* Evaporative Emission System (EVAP) Leaks: Leaks in the system that controls fuel vapor emissions can trigger the light.
* Crankshaft Position Sensor (CKP) Issues: This sensor is crucial for engine timing. A malfunction can prevent the engine from starting or running smoothly.
* Coolant Temperature Sensor (CTS) Problems: Incorrect temperature readings can lead to engine performance issues.
How to Diagnose:
The best way to find the exact cause is to have the OBD codes read by a mechanic or using an OBD-II scanner. The codes will give a much more specific indication of the problem. You can buy relatively inexpensive OBD-II scanners at most auto parts stores. Simply plugging the scanner into the OBD-II port (usually under the dashboard) will retrieve the diagnostic trouble codes (DTCs). Then you can look up the code online to get a better understanding of the likely cause.
Important Note: Driving with a check engine light illuminated can cause further damage. It's best to have it diagnosed and repaired as soon as possible. Don't just ignore it.
