A 97 Honda Accord LX 4 cyl car has engine light on. It has been scanned by the dealer. The problem is due to the faulty primary 02 sensor. So, the oxygen sensor has been replaced but the engine light is still on. I wonder whether the engine light is supposed to go off automatically after the replacement of the faulty oxygen sensor or it must be manually put into off or reset. Can you shed light on it? Thank you.

Clear the code by using a code reader or scan tool--this will certainly work. You can also try disconnecting the negative battery cable, or pulling the 7.5A Back-up Fuse in the under hood fuse box, for 10 seconds.

Thanks for reply. Got it how to do it. But, I still wonder whether the engine light should go off or not after the replacement of the faulty primary 02 sensor. It makes sense it should automatically go off after the replacement of faulty part. Isn't it correct?

Not necessarily. Many hard codes won't go away on their own, even after repairs are made. In the mean time, you may be adversely affecting performance.