The mass air flow (MAF) sensor (Figure 2) is a heated resistor type that indicates to the powertrain control module (PCM) the amount of air being allowed into the engine. The MAF sensor works by trying to keep a resistor at a constant high temperature. The temperature of the hot resistor is referenced with the temperature of a resistor that is held at ambient temperature. As air passes by the heated resistor, the temperature drops and the PCM compensates by allowing more voltage to the MAF. The more air that flows past the heated resistor, the more the temperature will change and cause an increase in required voltage from the PCM. This change in voltage indicates to the PCM that there is more air flowing through the MAF so the PCM can adjust fuel flow, ignition timing, and other outputs.