About a week ago, my CEL came on. After reading it was bank 2 sensor 1. I cleared the code and it was fine. After a week, about 300 miles later it came back on again last night. I didn't have a chance to re-read the code and the light disappeared this morning.

From the search, I know the code is for pre-cat sensor 1. Here are my questions:

1. Is it normal the light disappears itself? Is it really the O2 sensor or something wrong with my onboard computer?
2. If it is the sensor, which side is it? Some posts said it is the driver side and some said it is the passenger side.

Thanks.