Air Flow Meter/Sensor: Description and Operation

Air Mass Sensor:

PURPOSE
The Mass Air Flow Sensor (MAFS) is an electronic device mounted between the air filter and the plenum chamber. It serves as a key Engine Control Module (ECM) input, performing two functions: indicating the volume and temperature of air being drawn into the engine. These two factors allow the ECM to adjust the fuel supply accordingly.

OPERATION
Air density varies with temperature and altitude. Cold air is denser and contains more of the oxygen required for combustion. At higher temperatures and altitudes, more air must enter the engine to deliver the same amount of oxygen.

The MAF unit contains two wires with current passing through them. Both are connected to the module mounted on the MAF unit. One wire, which is unheated, reacts to intake air temperature. The second wire is heated to a known value of 212°F (100°C) above the unheated wire. As air flow increases, the current required to maintain this difference in temperature increases. The electronic module monitors this wire's current requirements to determine the amount of air entering the intake manifold. It then provides this signal to the vehicle's ECM.