For those who don't know, the MAF (mass air flow) sensor measures the mass of air entering the engine to control the air/fuel ratio. The sensor is incorporated into the intake system after the air filter. Bosch uses a hot-wire MAF sensor, which is a platinum wire heated to 212*F (some say 180*F) above ambient temperature. As air is sucked into the engine past the wire, it has a cooling effect that's offset by an increase in voltage to the sensor to maintain the 212*F. The engine management system then determines how long to keep the fuel injectors open. Upon shutdown, Bosch MAF sensors briefly heat the wire to 1,000*C to burn off any contaminants.