Why does the check engine light remain on with no performance problems? on 2001 Hyundai Elantra

I had my exhaust system replaced and my O-2 sensor replaced in the exhaust pipe.

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1 answer
There is most likely another problem with the car that is turning the check engine light on. We see more functioning 02 sensors repalced than any other part on a car.I would suggest you have someone diagnose the problem