Atmospheric pressure sensors are fitted at the engine air inlet to measure the air pressure that affects engine calibration. They are connected to a computer that reads the signal from the pressure sensor to regulate fuel trim and engine timing.
The atmospheric pressure sensor gives units in mmHg; this allows the computer to adjust the engine during changes in altitude. The computer does this by calculating the correct engine calibration for the conditions.
The atmospheric pressure sensors may fail because of their location, but this is indicated by the check engine light on the car’s dashboard. The location of the sensors varies with the model of the vehicle.