My 2009 E320 has a check engine light, a code 2633 (mass air flow sensor drift under engine load.) I also have a P2011, open or short circuit on a MAF sensor.
While diagnosing the issue, I discovered and fixed the following:

• Turbo intercooler hose had a crack / leak, replaced both hoses and pressure tested the turbo side of the system to 20 psi.
• PCV valve diaphragm was torn, replaced the assembly.
• Air filters were filthy, replaced them both.
• Replaced the turbo electronic actuator, don't know if it was bad or not.
• Replace air intake tube and MAF sensors, don't know if this was a problem or not.
• Replace the gasket between the PCV and the air intake.

I performed the following tests:

• Tested the intake flapper motor, works fine.
• Tested the MAF sensors, work fine.
• Tested the turbo actuator, works fine.
• Tested the EGR actuation, works fine.

I reset the following adaptations:

• "Quantity Mean Value Adaptation data".
• "Air Filter Learned Values".
• "Lambda Values."

At this point, the CEL persists with P2633 and the P2011 fault codes. I have run out of options to diagnose and investigate.
Does anyone have any suggestions? Many thanks from a desperate E320 owner.

 

Well, I tried the "Reset values for HFM Drift Compensation", and it appears to have solved the problem! It turns out "HFM" is an acronym for Hot Film Mass Air Flow Sensor, or MAF. Sure wish they'd use consistent nomenclature.

 

What did you use to reset adaptations? I am facing a similar issue with my 2009 E320 and have a Foxwell.

 

I use a Star Diagnostic system. I tried a few different scanners, but they didn’t do the job.