Originally Posted by Salty B.

I get it. I posted all the codes way upstream here when it happened a few months ago. I saw "AUC" and once I learned what it was from a commenter I ordered a new one. Before I replaced it, if I was behind a stank-ass diesel or other smelly exhaust it was definitely bad with the windows up. Now I might get a little whiff of it but it shuts the fresh air intake right away. Surprised to know it exists!