Here's the proper procedure:
1. Diagnose the Problem: The first and most crucial step is to determine *why* the CEL is on. You'll need to get a diagnostic trouble code (DTC). You can do this in a few ways:
* OBD-II Scanner: This is the best method. Buy a relatively inexpensive OBD-II scanner (available at most auto parts stores) and plug it into your car's OBD-II port (usually located under the dashboard). The scanner will read the DTC, which is a code representing the specific problem. Search online for the code to find out what it means.
* Auto Parts Store: Many auto parts stores will read the code for free.
2. Fix the Problem: Once you know the DTC, you can research the likely cause and fix it. This might involve:
* Replacing a faulty sensor: Oxygen sensor, mass airflow sensor, etc. are common culprits.
* Repairing a leak: Vacuum leak, exhaust leak, etc.
* Tightening a loose connection: A simple loose connection can trigger the light.
3. Clear the Code (After Repair): *Only after you've fixed the problem* can you clear the code. You can do this with your OBD-II scanner. Many scanners have a "clear codes" or similar function. Sometimes disconnecting the negative battery terminal for a few minutes will also clear the code, but using the scanner is more reliable.
Important Note: Simply clearing the code without fixing the problem will only temporarily turn off the light. The light will likely come back on, and the underlying issue could worsen, potentially causing serious damage to your engine.
In short: Don't just reset the light; fix the problem that caused it.
