A MAF sensor costs more than the scan.
The MAF should not invoke Limp Mode. I suppose it could, but I cannot form the logic in my head to support such a thing. A MAF is not a required part for simple engine operations. It is required for complex engine operations, and the complex operations would be needed to conform to emissions requirtements. The MAF reports the air density, and the information is used to modulate the fuel so that the proper air/fuel ratio of 14.7:1 is acheived and maintained. The O2 Sensors are used to fine tune the fuel mixture, and the inability of the O2s to fine tune the mixture is reported as RICH, LEAN, or MALFUNCTION. There are codes (FUEL TRIM and FUEL CONTROL, the latter being BMW codes in the P1 family) for these conditions. My car had a bad MAF, but it did not invoke Limp Mode. Indeed, my car had a bad MAF, and were it not for a host of other codes that appeared repeatedly, I would not have known there was anything wrong with the car. It ran perfectly, except that the Check Engi8ne light kept coming on.