* Oxygen Sensor (O2 Sensor) Malfunction: These sensors monitor the air-fuel mixture. A faulty sensor can lead to poor fuel economy, increased emissions, and the SES light illuminating.
* Mass Airflow Sensor (MAF Sensor) Problem: This sensor measures the amount of air entering the engine. A malfunctioning MAF sensor can cause incorrect fuel delivery, resulting in rough running and the SES light.
* Catalytic Converter Issue: This component reduces harmful emissions. A failing catalytic converter can trigger the SES light and may be accompanied by decreased performance.
* Spark Plugs or Ignition Coils: Worn-out spark plugs or failing ignition coils can cause misfires, leading to the SES light.
* Problems with the Exhaust System: Leaks in the exhaust system can disrupt the air-fuel mixture and trigger the light.
* Throttle Position Sensor (TPS) Failure: This sensor tells the engine control unit (ECU) the throttle's position. A faulty TPS can cause erratic idling and the SES light.
* Vacuum Leaks: Leaks in the vacuum system can affect engine performance and trigger the light.
* Low Coolant Level: While not always directly related to the engine's operation, a low coolant level can trigger the light in some vehicles as it's monitored by the system.
* Faulty Gas Cap: A loose or damaged gas cap can cause a small vacuum leak, triggering the SES light.
* Other Sensors: Many other sensors contribute to the engine's operation; a malfunction in any of them could trigger the SES light.
To find out the *specific* reason:
You need to have the car's OBD-II system scanned using a code reader. This will retrieve Diagnostic Trouble Codes (DTCs) that provide much more specific information about the problem. You can purchase a relatively inexpensive code reader from auto parts stores, or a mechanic can scan it for you. The codes will help diagnose the issue accurately.
