You're right, the wire colors from the O2 sensors don't match the Bently manual, but the wire colors between the ECU and the wire connector do. There are six of them going into the connector and the manual confirms this, I'm guessing it's supposed to connect to a 6 wire O2 sensor, right? If not, then what is that other wire for?

 

Bump.

 

Anyone know what that other wire/wire terminal is for? This is driving me crazy!

 

you said you have the manual and you said the manual does match the colors on the ECU side of the connector so look it up. it could be an unneeded wire or it could be something important.

 

It seems logical, that the O2 sensor that was last installed was the wrong type (5 wire instead of 6) except for the fact that it had the Audi logo on it. I find it hard to believe that it came from the factory with the wrong O2 sensor installed. Is there a better explanation of why the wrong O2 sensor would have the Audi logo on it? Where can I find the correct 6 wire sensor for my car if all the part sites list every 2001 A4 as having either 4 or 5 wire sensors?

 

I just found out that the extra wire is just an additional ground that doesn't connect to the O2 sensor despite its connection to the wire connector.

Thank you ghost6303, you've helped a lot.