Mass Air Flow (MAF) Sensor

Courtesy of VOLVO CARS CORPORATION

The mass air flow (MAF) sensor gauges the air mass sucked into the engine, regardless of the air's density and temperature. It continuously transmits signals to the engine control module (ECM) about the mass of the intake air. This data is used by the engine control module (ECM) to calculate:

• the engine load

The information is also used to determine:

• injection period
• fuel pressure
• the ignition timing
• turbocharger (TC) boost pressure (turbocharged engines only)
• Camshaft control (CVVT)

The transmission control module (TCM) also uses this data for its gear shift calculations. This data is transmitted to the transmission control module (TCM) from the engine control module (ECM) via the high speed side of the Controller area network (CAN).

The mass air flow (MAF) sensor consists of a plastic housing with connector and electronics as well as a sensor chip. The sensor chip is of a thin design, where two heat sensitive sensors are positioned in line and on each side of a heat generating sensor, one upstream and one downstream. When the chip is subjected to a flow of air, there is a temperature difference between the sensors, which is converted to a resistance difference. This is detected electrically by a so-called Wheatstone bridge, and is converted to mass air flow.

The mass air flow (MAF) sensor is supplied with battery voltage by the system relay and is connected to a 5 volt reference voltage and grounded from the engine control module (ECM). The signal from the sensor is analogue and varies between approximately 1-5 V depending on air mass. Low air flow (low mass) results in low voltage, high air flow (high mass) gives high voltage. No air flow gives a reading of approximately 1 V.

The mass air flow (MAF) sensor is positioned between the air cleaner (ACL) housing and the intake manifold.

The engine control module (ECM) can diagnose the mass air flow (MAF) sensor. The signal can be read using the diagnostic tool.