MAF and MAP Sensors

Automatic transmission sensors MAF and VSS.

The ECM and the TCM monitor engine load 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 affects 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 sensor that indicates engine load and that also affects shift timing is the MAF sensor.

A (MAF) mass air flow sensor measures the volume of air passing through the air tube. 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 sensor utilizes a potentiometer (variable resistor) 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. The ECM increases and decreases current as cool air flows through the filament. The current used to maintain the sensor's heat is converted into a voltage signal and sent to the PCM to make adjustments to the air-fuel ratio.

A wiggle test to check to see if a mass air flow sensor is loose or unplugged

Both the MAP and MAF sensors provide the PCM and TCM with valuable engine load information. The transmission's control unit uses this information for shift control.