I did not have a check engine light and the check engine light bulb does work.

I was clearing a code on another car and I thought I'll check the 1999 ML 320. The code is fuel trim malfunction bank 2. And like I said I have no CEL. I cleared the code without any problem.

What might be going on. The vehicle runs perfectly.

Edited:

My guess is MAS going bad, however, I don't want to spring for $310. if I don't really need one.