ThirdEye

I was reading the how to for replacing the o2 sensor and they were referring to the 3 wire version not the 4 wire version because the A4 12valve had a 3wire sensor and I accidentaly bought the 3 wire version even though my car has 4wire. My old sensor had 2 white, 1 black and 1 gray cable and the new one had the same except it was missing the gray one. I read that the extra cable is just a ground so I hooked up all the cables coming from the ECU correspondingly to the 3 wire o2 sensor and grounded the extra cable from the ecu to the negative terminal of the battery because I read here that it is just a ground cable. Now I have a check engine light. Can someone please advise on what to do and what I did wrong? Thanks!

OttawaA4Can

you can connect it to any solid part of chassis.. the entire chassis is ground.... dont' know if this will help...

birdsong

Heh, and the ground runs back to the negative side of the battery. One and the same, really.

Audi2ptzero

Go buy the correct 4 wire sensors.