Air Flow Meter/Sensor: Description and Operation

Air Cleaner And Air Mass Sensor Assembly:

Air Mass Sensor:

The air mass sensor, located on the air cleaner housing upper section, measures the flow of air into the engine without the use of moving parts that interfere with the air flow. Unlike a flap type air flow sensor which only measures the volume of air flow, an air mass sensor measures the actual mass per unit time of air entering the engine. This is a more accurate means of measurement because any given volume contains different quantities of air depending on the air density.

In the air mass sensor, a platinum wire filament, protrudes into a small venturi in the center of the sensor housing. The wire is heated by an electrical current. As intake air passes over the hot wire, the wire is cooled causing a decrease in the resistance. When this happens, more current is required to maintain the hot wire at the reference temperature (approximately 356~F/180~C above the intake air temperature). The more air that enters the intake system, the greater the cooling effect on the hot wire and the more current is required to maintain the wire at its reference temperature. The ECU measures the current through the wire and calculates the mass of air entering the engine. The result is then used to determine the amount of fuel needed and the base pulse width for the fuel injectors to maintain the correct air/fuel ratio. For more specific information on the air mass sensor, refer to COMPUTERIZED ENGINE CONTROLS.