* To clear a check engine light (CEL): The CEL indicates a problem detected by the PCM. Simply disconnecting the battery won't fix the underlying issue. *Clearing the code only removes the light, not the problem.* You need to diagnose and repair the cause of the CEL. You can do this in a few ways:
* OBD-II Scanner: This is the best option. An OBD-II scanner (available at auto parts stores) will read the diagnostic trouble codes (DTCs) stored in the PCM, telling you exactly what's wrong. After repairing the problem, you can then clear the codes using the scanner.
* Auto Parts Store: Many auto parts stores will scan your car for free and give you a print-out of the codes. They can also help you interpret them.
* Mechanic: A mechanic will diagnose and repair the issue professionally.
* To reset the PCM after a battery disconnect or repair: After disconnecting the battery, sometimes the PCM needs a few drive cycles (start the car, drive for a while, turn it off) to relearn its parameters. This is normal. You don't need to do anything special, just drive the car.
* To reset a specific system (like the radio): Many systems in the car have their own reset procedures. For example, the radio may have a specific button combination or procedure. Consult your owner's manual for instructions on resetting individual components.
* To perform a "hard reset" of the PCM (generally not recommended unless advised by a mechanic): This usually involves disconnecting the battery's negative terminal for a longer period (sometimes up to an hour), or even disconnecting the PCM itself (this requires expertise and should only be done if absolutely necessary). This is an advanced procedure and is not recommended for average users. It can erase important learned parameters.
In short: Unless you have a specific problem that you need to solve (like a CEL), you likely don't need to "reset" anything. If you have a problem, diagnose it first (using an OBD-II scanner is best) before attempting any resets. If you're unsure, consult your owner's manual or a qualified mechanic.
