Hyundai Repair: oxygen sensor, oxygen sensor, trouble code

Question
99 Elantra, check engine light on, code indicates downstream sensor bad.  Replaced sensor, still get the check engine light and the same daignostic code. The car has 95,000 miles and runa fine.

Answer
Please follow up with the trouble code you're receiving.  The trouble code will tell my what the ECM thinks is the problem with the downstream sensor.

I'm presuming you cleared the code and it came back within a day or few of driving.  If not, you need to clear the trouble code.