so my 98 cherokke was running ok but rattling by the cat so i took it in and the shop said i needed a new cat. so i got one installed but ever since then i keep getting o2 sensor codes and it for the front one mostly. so i went ahead and got one from the dealership and had it installed. but the code still pops up and it usually the day after i cleared the codes. and every once in a while the reader will pick up the back o2 but the shop told me that that one is fine. so my question is could the cat that was installed the wrong one or is my computer bad? or are there any other things i should check out before replacing the computer. thanks for your help.

 

I would guess a problem with the converter.

 

The two O2 sensors compare data, if one is new and one is old and covered with carbon and who knows what, It will fail and set a code because the system is not working correctly. the measurement between the two sensors is so far out of spec it sets a code. O2's should be replaced in pairs. depending on the year of the vehicle some have two some have four sensors.

 

They have diffrent converters for CA emissions and fedral maybe they put on the wrong one