The car is a 99 Civic Ex coupe, i was throwing a code for the catalyic converter. I replaced it with good used 96-98 civic ex oem cat. After driving a few miles i threw the same cataylic converter code again. I'm sure the cat i bought was good, is it my 02 sensor? Does it need to be replaced? Or am i still throwing a code becuz i'm using a 96-98 cat? I checked the part #'s on both 98 and 99 civic ex 02 sensors and they are both different. LMK thx guys

 

well can u see through the cat? if not its bad. u might think u bought a good one vbut it could be bad. anything used = un sure of quality

 

Check for an exhaust leak.

 

sh#t i forgot that can do it to

 

thx for the input guys, i'm doing a brake job today so i'll check for both things you guys mentioned.