Mass Airflow
Air mass entering the induction system is measured by the MAF sensor. A ceramic resistor is used to measure incoming air temperature. Incoming air cools the sensing element. Measurement of electrical power to maintain the MAF sensor ceramic resistor at 165°F (75°C) above the incoming air temperature determines the air mass. See Fig 1 and Fig 2 .
The electrical power requirement is measured and converted to a digital signal (30-150 Hz), which is then sent to the ECM. This is then used to determine engine load.
Using calculations of mass airflow, engine temperature and RPM, the ECM calculates the fuel requirement to provide a proper air/fuel ratio of 14.7:1.
Some MAF units are the Bosch hot wire type. This type contains a sensing wire. Current is supplied to maintain a calibrated temperature. Current varies with amount of airflow. Current changes are processed by the ECM to provide proper air/fuel ratio.
The sensing wire contamination is prevented by heating sensing wire to 1000°F (538°C) after engine shutdown. This burn off cycle is controlled by the ECM. If burn off cycle did not occur, the Service Engine Soon light will activate and stay on after next engine start.