ok, ima give some more insight to hopefully find a solution for this problem. on the first sensor, as soon as i reset the ecu it would immediately throw the code. now with the new sensor, it waits about 3-5 seconds then shows up sayin the same code 65. heres a thought i just had. what are the signs of a cat goin bad? i have a catco hi flo cat(on there since july 04) BUT, i did notice somewhat of a sulfar smell sometimes under somewhat heavy acceleration, and i did also notice a rattling sound between 2500 - 3000 rpms. could a potentailly bad cat cause this code to come up?