Common Problems:
* Oxygen Sensor(s) (O2 Sensor): These sensors monitor the exhaust gases. A failing O2 sensor can cause poor fuel economy, rough idling, and trigger the check engine light. This is very common on older vehicles.
* Mass Airflow Sensor (MAF Sensor): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can lead to poor performance, rough running, and the check engine light.
* Catalytic Converter: A failing catalytic converter can cause reduced engine performance and trigger the light. This is more likely on higher-mileage vehicles.
* Spark Plugs and Ignition Coils: Worn spark plugs or failing ignition coils can cause misfires, leading to the check engine light.
* PCV Valve (Positive Crankcase Ventilation): A faulty PCV valve can cause excessive crankcase pressure, leading to various engine problems and the check engine light.
* Throttle Position Sensor (TPS): A malfunctioning TPS can affect engine performance and fuel delivery, triggering the light.
* Crankshaft Position Sensor (CKP Sensor): This sensor tells the engine's computer where the crankshaft is. A bad CKP sensor can prevent the engine from starting or running smoothly.
* Low Fuel Pressure: Issues with the fuel pump or fuel filter can result in insufficient fuel pressure.
* Evaporative Emission System (EVAP) Leak: A leak in the system that controls fuel vapors can trigger the light.
Less Common, but Still Possible:
* Transmission Issues: While less common to directly trigger the check engine light, transmission problems *can* sometimes set a code.
* Wiring Issues: Damaged or corroded wiring can cause intermittent problems and trigger the light.
* Sensor Failures (various): Many other sensors contribute to the engine's operation. A failure in any of them could trigger the check engine light.
To find the exact cause:
You'll need to have the diagnostic trouble codes (DTCs) read. This can be done in a few ways:
* OBD-II Scanner: Buy a relatively inexpensive OBD-II scanner (available at most auto parts stores). Plug it into the OBD-II port (usually under the dashboard) and it will read the codes.
* Auto Parts Store: Most auto parts stores will read the codes for free.
* Mechanic: A mechanic will have the tools to read the codes and diagnose the problem.
Once you have the DTCs, you can look them up online or in a repair manual to determine the likely cause of the check engine light. Do *not* just assume what the problem is based on common causes. Getting a code read is the most important first step.
