<Li> in some manufacturers fuel pump control was also part on the VAF internal wiring . </Li> <P> A hot wire mass airflow sensor determines the mass of air flowing into the engine's air intake system . The theory of operation of the hot wire mass airflow sensor is similar to that of the hot wire anemometer (which determines air velocity). This is achieved by heating a wire suspended in the engine's air stream, like a toaster wire, with either a constant voltage over the wire or a constant current through the wire . The wire's electrical resistance increases as the wire's temperature increases, which varies the electrical current flowing through the circuit, according to Ohm's law . When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit, since the supply voltage is a constant . As more current flows, the wire's temperature increases until the resistance reaches equilibrium again . The current increase or decrease is proportional to the mass of air flowing past the wire . The integrated electronic circuit converts the proportional measurement into a calibrated signal which is sent to the ECU . </P> <P> If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow . Unlike the vane meter's paddle sensing element, the hot wire responds directly to air density . This sensor's capabilities are well suited to support the gasoline combustion process which fundamentally responds to air mass, not air volume . (See stoichiometry .) </P> <P> This sensor sometimes employs a mixture screw, but this screw is fully electronic and uses a variable resistor (potentiometer) instead of an air bypass screw . The screw needs more turns to achieve the desired results . A hot wire burn - off cleaning circuit is employed on some of these sensors . A burn - off relay applies a high current through the platinum hot wire after the vehicle is turned off for a second or so, thereby burning or vaporizing any contaminants that have stuck to the platinum hot wire element . </P>

Where is the mass air flow sensor located