I had my exhaust system replaced and my O-2 sensor replaced in the exhaust pipe.
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2001 Hyundai Elantra Question: Why does the check engine light remain on with no performance problems?
Answer #1donsauto from Don's Auto Repair, Inc., July 06, 2011, 10:35Enthusiast
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