Air Flow Meter/Sensor: Description and Operation

MASS AIR FLOW SENSOR

The Mass Air Flow Sensor (MAF) is an electronic device mounted between the air filter and the plenum chamber. It serves as a key ECM input indicating the volume of air being drawn into the engine. This allows the ECM to adjust the fuel supply accordingly.

Air Density:

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.

Mass Air Flow Sensor:

The unit contains a wire with current passing through it. The wire is connected to the module mounted on the MAF unit. The wire is heated to a known value of 100°C (212°F). 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.

Typical MAF output voltage at idle is between 1.3 and 1.5 VDC. A diagnostic trouble code is produced if MAF voltage is:

- Less than 122 mV with RPM in excess of cranking speed.

- Greater than 4.96 Volts with RPM less than 976 for more than 160 milliseconds.