Hello all I have been having yet more trouble with my 2002 Blazer. 4 door ok I had a friend of mine hook his computer up to it due to the check engine light being on. It came back that the system was too lean in Bank one and Bank 2. The consensus here in the office is the o2 sensor the mileage is about 125K. OK here is my quest there are 4 O2 sensors which two do I change the ones before or after the catalytic converter or after?
Thanks
Andre

 

The O2 sensors in front of the Cats feed back information to the computer to control the mix. The O2 sensors after the Cats are to check the efficiency of the cats. With that many miles you likely need all of them. Have any of the O2 sensors ever been replaced?
Hope this helps.

 

Yeah, sounds like you should just replace them all if you have never replaced any of them.