I have a 854t and had the front 02 replaced. I bought it online and it was preharnessed and fit no problem.. i had the shop put it in since they were doing something else to the car. I was before getting constantly 425 and 435 errors. Now with the new one I get 153 and 212 which I believe means that they are both missing. I removed the harness and reinserted it in case it was making a bad connection but it looked fine. The company i bought it from also told me some checks to do. I've resetted the computer many times since it takes only around 50 miles to trigger the code. I also had previously many of the vacuum lines and elbows checked and/or replaced. The engine now also will rev to 2k at startup for a couple of seconds and then settles to its 900. The car drives well and I do think the mpg has increase a tiny bit. Any thoughts on this?? Bad sensor? I kept my old sensor and was thinking of doing the clean job on it with the brake cleaner and torch as I read before on the brickboard.