Wow I learn something new every day :-)

Dear Mr. Brotherton: your reply really solves one of the puzzles that I faced, because I always got the long-term fuel trim value of (-18%) using my OBDII scanner. I thought it might be a bug in my OBDII scanner. In some of your posts in other threads, you mentioned something about the ability of Mercedes control units to make a correction of as much as -32% or +32%, while I could only get a LTFT of -18% from my car. Now everything is clear: my car must have an early control unit that can only make a correction down to -18% and up to 18%. Thank you very much for that precious piece of information!

Many thanks to M.B.DOC, Kebowers, and Steveblf for your expert replies. I will send my complaints to the Ebay seller regarding the HOT WIRE MAF. I should expect a HOT FILM MAF only (anyway, that's what HFM stands for :-)

From your extensive experience working with Mercedes cars, what are the average corrections on a new Mercedes and an used working Mercedes? Is a 0% correction very commonly seen? If a car is running with a correction of as much as -30% or +30% (supposedly with new control units), is it still considered as being in good shape?

Are you aware of any "hack" that allows the resetting of the HFM-sfi unit without using a Snap-on MT2500 or a SDS?

Many thanks again.

Best regards,

Eric