Mass Air Flow Sensor
A MAF (Mass Air Flow) sensor measures the volume of air passing through the air tube. There are three types found on vehicles today. These include the cold wire, hot wire, and the vane type MAF sensors.
The vane type uses a paddle or door that moves as the air rushes by. This type of sensor utilizes a potentiometer (variable resister) to send a variable or changing voltage signal to the ECM in proportion to air volume.
The cold wire MAF sensor uses thin metal strips that vibrate as the air passes by. This vibration changes in frequency as does the signal sent to the ECM.
The hot wire MAF sensor has a heated filament like a toaster. The sensors resistance changes or decreases as cool air passes by the filament. The increase in current is converted to a voltage signal and sent to the ECM to adjust fuel trim.
Most MAF sensors have an internal IAT (Intake Air Temperature) sensor located inside of the sensor. The ECM uses the MAF sensors signal along with temperature and pressure signals to make accurate fuel air adjustments while in open loop. These signals used in correlation with the closed loop signal from the oxygen sensor provide extremely accurate fuel trim conditions (14.7:1) stoichiometry.
The MAF sensor provides the ECM and TCM with valuable information regarding engine load. The transmission control unit uses this information for shift control. A bad or unplugged MAF sensor will effect a vehicles shift control dramatically.
