Air Flow Meter/Sensor: Testing and Inspection

Comprehensive Component Monitor - Mass Airflow Sensor

The Mass Airflow (MAF) Sensor (MAF) assembly outputs an analogue voltage to the ECM. This sensor measures air flow into the engine intake system and is calibrated to measure kg/hour.

The MAF sensor contains a hot wire resistance element that forms part of a Wheatstone bridge. Air flowing around the hot-wire cools it, so altering the value of its resistance. The consequent change in the voltage dropped across the resistance is compared with the voltage dropped by the other resistance arms of the Wheatstone bridge to determine the airflow. This signal is input to the ECM.

The MAF sensor is continually monitored by OBD routines. A DTC is recorded if the input signal from the sensor to the ECM is outside pre-defined thresholds at the high or low end of the scale.

The MAF sensor is supplied with a regulated ground reference from the ECM. A ground feedback path is also supplied via a separate pin to the ECM. If the ECMs OBD identifies a drift of greater than 1 volt above actual battery negative on the ground feedback for longer then a defined period then a ground open circuit fault is logged.

Actual MAF entering the engine is compared with data stored in the ECM memory for ideal airflow under stable throttle conditions. Compensation is made for altitude. If the difference between actual and ideal airflow is greater than a calibrated value, a DTC is stored in the ECM.

Note: Unless specifically included in the tables below, IAT, ECT, vehicle speed and time after start up are not critical to enable these monitors.