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Can anyone melp me understand the mass air sensor. My repair man wants me to buy one and I read that it cna be cleaned or repaired.
 

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2004 SL55 AMG
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[8D]
M-B uses a hot wire mass air sensor. In theory, the operation of it is simple and bulletproof. A thin wire is heated by passing electricity through it. Intake air rushing over the wire cools the wire. The more air flow, the cooler the wire gets. Since the electrical reistance of the hot wire is a function of the temperature of the wire, measuring the electrical resistance of the wire provides a measurement of the amount of air flowing by (the mass of the air flow in cubic feet per second, or whatever units you like).

I reality, these systems can fail in a number of ways: the wire can break, the wire can get covered in carbon deposits (from an overly-oiled K&N air filter, usually), the circuit that measure the wire's resistance can go flaky, and on and on.

Cleaning carbon off the wire is difficult, almost impossible in some cases, because toasted carbon is as hard as ceramic. If you use a tool or grit paper hard enough to remove the carbon, you'll take some of the wire metal too. Then, the circuit that measures the resistance will be AFU, because the wire's properties have changed.

Sorry if that's more than you ever wanted to know. Good luck with it. And...

Happy Tax Day,
Dave
 

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Discussion Starter #3
Thanks I understand it better now. My wrench wants me to purchase an assembly containing the MAS, because he says it is the best way to go. My parts guy says the assembly is $850 ($List 1200). Do you agree that this is the best way to go?

Billy
 

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2004 SL55 AMG
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Good question, but I'm no position to answer; I don't have the car in front of me with a repair manual and a test bench. Depends on how much you trust the mechanic's diagnosis.

Is he just swapping modules because that's what he knows how to do? Or did he trace through the diagnostic codes and run the tests to prove the MAS-containing module is the culprit?
 

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Depending on your year MB , you could find a TESTED used unit at 30- 40% of new . I bought one for $ 90 US with a new unit costing $ 268 . I wish I could remember the Name ,But It was in Connecticut I found it on an MB-parts - used-junk yard ??? ////// search .
 
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