Hello everyone. I'm new to these forums and new to Audis in general. I recently purchased a 2001 Audi A4 and have had a few issues and need some help. First off, everytime I accelerate hard my car makes a high pitched whisting noise. It goes away after a few seconds. Also, my check engine light came on and I got it checked out. I have an o2 sensor that needs replaced. Could these be related in any way? Also, what is the cost to get an o2 sensor replaced at the shop. Any help would be really appreciated!

 

The secondary air pump would have gone bad.

 

The whistling can be from your turbo or 2nd air pump. Which 02 sensor do you need? Upstream or downstream? I know upstream is $250 cuz there's another sensor with it. Downstream I dont know the price for you.