This was an easy fix – BUT I wanted to share how an aftermarket scan tool can improperly display Mercedes Benz fuel trim faults and values. We will look at it using a Snap On MODIS (same scanner software as all their models) using generic and Mercedes Specific software.

The following fault codes were stored.

Generic

Mercedes Specific

Scan data

Generic

Mercedes Specific

As you can see the values are flip flopped depending on which version of the scan tool I was using. What’s important is to check when the fault codes set and specific fault code definitions.
Additive or idle load will likely be vacuum leak.

Multiplicative or part load will likely be fuel delivery issues. ie. MAF, fuel pump.

Oh, you wanted to know the fix. After the MAF sensor mounted to the intake duct to throttle body there is a rubber hose. It is very common for this hose to crack and swell from oil contamination.