I have a 99 SE and my check engine light recently came on. I had the test run and they said that it was the Oxygen sensors and that I should change both of them. I went out and bought 2 Denso sensors. The guy at the shop told me that both of them were the same part number. The one in the exhaust manifold plugged into the harness perfect. The other didn't fit where it was supposed to. My question to the Org. is did the dude at the shop bs me and sell me a wrong part or did I just try to put the rear sensor in the wrong place? I don't want to go back to the store and be ****ed at him if I do not have to. Anyone have any pics or diagrams on where the 2nd sensor should go?

 

there are THREE of them two go into the YPIPE under the connecting flange and one is buried inside the cat. Some more info would help

 

I guess that I am all mixed up.... The guy at Olympic Auto Parts in Greenbelt, Maryland told me that my Max only had 2 sensors. When I got under the car I saw that there was a 3rd. I usually take the word of these guys because they have never led me in the wrong direction. I guess that I should have posted here before I bought the parts. I changed the sensor under the hood on Sat. and the CEL was still on, but then this morning I started the car to warm it up and the light was off. Does this mean that only on sensor was faulty?

 

http://www.courtesyparts.com/A32_O2-sensors.html You have 2 sensors in the front (on the y-pipe, under the engine) and you have one by the cat (under the passenger seat area).

The 2 in the front should be the same (only the length of the wire is different), but the rear one is different from the front ones. The front 2 sensors have 3 wires on each sensor. The rear sensor has 4 wires.

 

My set up is totally different from that...I will have to take some pics when I get home and post them. Your diagram looks like a whole different car to mine.