Air Flow Meter/Sensor: Description and Operation

Mass Airflow Sensor G70

A port in the Mass Airflow (MAF) sensor measures a small portion of the air flowing through the intake system. This measurement is used by the Engine Control Module (ECM) to help calculate engine load and injector duration. The ECM calculates a substitute value from the engine speed and throttle valve position.

The MAF sensor measures the number of air molecules entering the engine (volume) and how tightly they are packed together (density). Some MAF sensors also contain the intake air temperature sensor (G42).

Later MAF sensors have reverse airflow detection. When the intake valves and/or the throttle plate close, the air path reverses and sends the air back across the MAF sensor. This causes the air to be measured a second time, resulting in an incorrect load signal. To prevent this, later MAF sensors use reverse airflow detection. Reverse airflow detection used the temperature sensors in the MAF to measure the direction of the airflow.