Last August 03, I brought the car in the dealer for ENGINE LIGHT check. They told me I need to replace both cats for $3400. So, I went ahead bought dealer part $900.00 just for 1 item, and replace this on the left side (below driver side). Few weeks later, I cleaned battery connector and left cable off for 30mins. The Engine light went away until now, Feb 04. So, I am not sure. it's really the cat or sensor at this moment after I got the code pulled from AUTOZONE. I am very confident with the code was pull at the Autozone, because they got it right on last Engine Code error. Can you give me some hints on how to mearsure the sensor? does it have to be removed from the pipe before do the measurement? Thanks LExv8