CEL on
 

Hi all

I have a dilemma I hope somebody can help me with. I purchased a 2001 Elantra real cheap so I know some work needed to be done on it. CEL is on from the pre-cat and post cat O2 sensors according to my mechs. scanner. I replaced both and also discovered a leak with the font exaust pipe, so that was replaced. The check engine light still is on after the car warms up-my mech. scanned it and it is showing bad post cat. sensor-my question is there any other possible issues or is it that I just may have gotten a bad O2 sensor. Could it also be possible that there is risidual material (Carbon) that is sending the sensor the wrong mixture quotient, since it has been running on for quite some time and just needs to be re-set numerous times until it doesn't come on anymore?
I did clean off the ground, but possibly I may have missed one. Could this be a wiring issue? any help/suggestions appreciated