check engine soon on 2002 Nissan Pathfinder

the light came on and I have had several items changed. It came on agin, but this time the car was at idle for about 10 minutes.
I have heard there are 2 02 sensors. culd it be the garage changed only one?

1 answer 2 comments
If you have had your car into a garage for a check engine light, and they are replacing parts and the light keeps coming on, you need to go to another garage. A good diagnostic technician will identify the root cause in the emission control system that is leading to the trouble code throwing the check engine light, and he will fix that underlying problem.

A poor diagnostic tech will start replacing parts in reaction to the codes without identifying what is wrong--that gets really expensive!
sorry if I misstated, but the tech repairs according to codes. He is not just trying this or that. there have been 3 different codes and each time the light goes off,but after 2 or 3 hours of driving and then idling, the light comes back on. we even did a smoke test.
I understand. This still means that the technician doesn't know what the problem is, and he is chasing codes.