Here's the proper procedure:
1. Diagnose the problem: The first step is to determine *why* the CEL is on. You have a few options:
* OBD-II Scanner: The best approach is to use an OBD-II scanner (available at most auto parts stores). This will read the diagnostic trouble codes (DTCs) stored by the computer. These codes provide clues about the specific problem. You can even find inexpensive Bluetooth OBD-II scanners that work with smartphone apps.
* Auto Parts Store: Many auto parts stores will read the codes for free. They can sometimes offer suggestions, but don't always rely on their diagnosis.
* Mechanic: A qualified mechanic can properly diagnose and repair the issue. This is the most reliable, though most expensive option.
2. Repair the problem: Once you know the DTC(s), you can research the likely cause (online forums, repair manuals, etc.) and attempt a repair yourself *or* take it to a mechanic. Fixing the underlying issue is crucial.
3. Clear the code (after repair): *Only after you've repaired the problem* should you attempt to clear the code. You can do this in a couple of ways:
* OBD-II Scanner: Most OBD-II scanners have a function to clear diagnostic trouble codes.
* Disconnect the battery: This is a less reliable method. Disconnect the negative (-) battery terminal for about 15-20 minutes. This will often clear the code, but sometimes doesn't clear all codes or may reset other computer settings. Reconnect the battery and start the vehicle.
Important Note: If the CEL comes back on after clearing it, the problem hasn't been fixed. Return to step 1 and repeat the process.
In short, resetting the light is the last step, not the first. Focus on finding and fixing the cause of the problem. Ignoring the check engine light is strongly discouraged.
