I only seen 1 o2s for each manifold, P1131 bank 1.I think this is firewall side. When I called for the part, I was asked, up stream or down stream, the sensor had 2 white wires 1 black and 1 grey, I did my bench test with the black wire and I used the sensor end for ground volt-meter dc volts, did I do that right? Did this guy know what he was talking about, is there 2 o2s for each exhaust manifold, upstream and down stream because, I sure didn't see this. Will you also tell me how to do the bench test? Thanks a lot!