I had my wife go to gm dealer today and get a oil change, we have a 08 trailblazer with 47,000 miles, they showed her the airfilter was dirty so she had them put it on (I could have done it myself) anyway they charged her $91.76 for oilchange and filter, way to much, now they tell her the oxygen sensor is going out, and the part cost $161.21 plus labor, I got on Rock Auto and its $34-80 dollars, now my question can i do it myself, wheres it located, and do i have to do something after its installed, oh by the way theres no lights on so i dont know how they say it needs this. We still have a warratee on this truck