I bought a 2001 accent about a month ago off a friend. There was nothing wrong with it when I got it. A week later the check engin light came on so i got a diagnostic ckeck done. showed the o2 sensor before the cat. i bought a new one and replaced it myself and reset the computer. the next week the light came on again so i took it to a dealership. the said the reason the one i put in was because it was an aftermarket sensor. i got it back 4 days ago from them and the light came back on, ran 2 more diagnostics checks today showing o2 sensor(bank 1 sensor 1). could there be anything else causing this problem

 

I am having the same problem!! I had my check engine light come on saying that the sensor in Bank 1 Sensor 1 is bad. So i replaced it with a Boche O2 sensor from advance auto. As soon as i started the car after replacing Both o2 sensors the light came on. i took it to adavance auto and they reset the light with the OBDII computer scanner and thought it may have freaked out since i put a new one in it. I drove not even 2 miles to the house and the Check engine light came back on.

Anyone have any sugestions??

2001 Hyundai Tiburon