o2 senesors have to be on exaust manifold so where ,thats the only place it can positively check co2/feul emissions On the back side of the engine (between the engine and the firewall) there is a cover with 3 bolts in it. Remove the 3 bolts and the cover and you will find the exhaust manifold with the O2 sensor. You will need a 7/8" wrench to remove it and install a new one.