When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Bank one sensor one and bank two sensor one are upstream O2 sensors and are forward of the cats. B1S1 is passenger side. B2S1 is driver's side. There are two downstream of the cats as well.