We have not yet encountered a dealership or service provider with test equipment necessary to determine if a MAF sensor is functioning properly; nor do they have the test equipment to determine the cause of a failure. Therefore, the diagnosis of a failed MAF is an educated guess.  For information on our test procedures and findings click here.  Nowhere is their lack of care in this regard more evident than in an actual Technical Service Bulletin published by a major American vehicle manufacturer that directs mechanics to "test" a sensor by removing it from the problem vehicle and placing it in a functioning vehicle of the same type. If the problem recurs in both vehicles, the sensor is to be diagnosed as the problem. If you are a mechanic, and you have a broken 2003 vehicle in front of you, how often will you even have access to a properly functioning 2003 vehicle of the same type? In light of such "technical" support, it is no wonder most mechanics revert to hearsay and educated guesses and never even attempt to complete the manufacturer's test. This is why we believe such a high percentage of the sensors we recover are not damaged at all.