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.
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.