MAF and MAP Sensors
Engine load is monitored by the ECM and the TCM through the MAP and MAF sensors. The (MAP) manifold absolute pressure sensor senses engine load through pressure in the intake manifold. A faulty MAP sensor will really affect engine performance, but can also affect transmission’s shift timing. This is because the PCM uses this signal as an indication of engine load. Another important sensor used to indicate engine load and also has an effect on shift timing is the MAF sensor.
A (MAF) mass air flow sensor measures the volume of air passing through the air tube to indicate engine load. There are several types found on vehicles today. These include the cold wire, hot wire, Karmen Vortex and the vane type MAF sensors.
The vane type MAF sensor uses a paddle or door that moves as air rushes by. This type of sensor utilizes a potentiometer (variable resister) to send a variable or changing voltage signal to the PCM 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; changing the signal sent to the PCM.
The hot wire MAF sensor contains a heated filament similar to a toaster element. Its resistance changes or decreases as cool air pass by the filament. The changes in current to maintain the sensors heat are converted into a voltage signal and sent to the PCM to make adjustments to air fuel ratio.
Both the MAP and MAF sensors provide the PCM and TCM with valuable information regarding engine load. The transmission’s control unit uses this information for shift control. A mass air flow sensor left unplugged or in need of cleaning (hot wire) will affect a vehicle’s shift control dramatically.