To find out *why* the light is on, you'll need to get the diagnostic trouble codes (DTCs) read. This can be done a few ways:
* OBDII Scanner: The most reliable method. You can buy a relatively inexpensive OBDII scanner at most auto parts stores. These scanners plug into a port usually located under the dashboard (often near the steering column) and will display the trouble codes. This will give you a much better idea of the problem.
* Auto Parts Store: Many auto parts stores will read the codes for free. They'll plug in their scanner and tell you the codes. Be aware that they may try to sell you parts based on their diagnosis, but you're not obligated to buy from them.
* Mechanic: A mechanic will be able to read the codes and diagnose the issue. This is the most expensive option, but offers the most comprehensive solution.
Possible Causes (without knowing the codes):
The SES light in a car that old could be triggered by something as simple as a loose gas cap, or something as serious as a failing catalytic converter or oxygen sensor. Some common possibilities include:
* Oxygen Sensor: Measures the amount of oxygen in the exhaust. A faulty sensor can cause poor fuel economy and emissions problems.
* Mass Airflow Sensor (MAF): Measures the amount of air entering the engine. A malfunctioning MAF sensor can lead to rough running and poor performance.
* Catalytic Converter: Reduces harmful emissions. A failing converter can cause poor performance and trigger the SES light.
* Spark Plugs or Wires: Worn spark plugs or faulty ignition wires can cause misfires, leading to the light.
* PCV Valve (Positive Crankcase Ventilation): If this valve is clogged, it can cause excessive crankcase pressure and affect engine performance.
* Throttle Position Sensor (TPS): Sends information about the throttle position to the engine control unit. A faulty TPS can cause poor drivability.
* Loose or Damaged Gas Cap: Surprisingly common, a loose or damaged gas cap can trigger the light due to evaporative emissions.
Don't ignore the light. Driving with a malfunctioning system can lead to further damage or cause the car to fail emissions testing. Get the codes read as soon as possible to pinpoint the problem.
