Well, give us some info here. What kind of Benz (year, make, model) do you have? Is it super/turbocharged or nautrally aspirated? These will tell whether you have a MAP or MAF, while both are 'air metering' devices, the both work quite differently.
If neither were working the one thing you could count on would be a CEL on the dash readouts. You could then go get your code pulled at the local Autozone, etc. and you would know if it was or not.
What kind of problems are you having? What makes you say it might not be working?
If your MAP/MAF is not working, you will get some kind of MIL. Whether its from improper A/F ratio, the actual sensor not working, or an affect of said sensor not working, you will get a MIL. It will trip something in the ECU that will trigger a MIL.
Whether or not you will realize it because it may seem unrelated is another story.
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