Air Flow Meter/Sensor: Description and Operation

PURPOSE
The mass air flow sensor provides the ECU with continuous information regarding intake "air mass."

LOCATION
Mounted on the air cleaner housing, top cover.

CONSTRUCTION
The mass air flow sensor is a hot-film sensor type with 4 resistances. The unit consists of a plastic housing containing a connector, electronic circuitry, and an aluminum heat sink.

Each film resistance performs a different function:
Rt, Temperature sensitive NTC-type resistance signal. Supplies information regarding intake air temperature.
R1, Calibration resistance.
Rs, Flow sensitive PTC-type resistance signal. Also supplies information regarding the cooling effect of intake air.
Rh, Heating resistance. Maintains the temperature of Rs at 340°F (170°C) above intake air temperature.

OPERATION
The mass air flow sensor uses an electronic unit to measure the current required to maintain the temperature of Rs at 340°F (170°C) above intake air temperature.

The flow required to maintain the temperature constant is proportional to the mass of air flow. The electronic unit measures the quantity of current required to maintain the Rh resistance at a constant temperature above the Rs resistance.

This current is converted into a signal voltage, varying between 2.6 volts (at idle) and 8.0 volts (at wide open throttle). The signal is transmitted to the LH control unit.

Since any contamination will deposit on the front of the plate (leaving the film clean), there is no need for a burn-off function as is required on the hot-wire type.