Air Flow Meter/Sensor: Description and Operation

GF07.07-P-6000MLK Hot Film Mass Air Flow Sensor, Component Description
- refinement package
- as of model year 09

Component Identification:

Location
The hot film mass air flow sensor is located behind the variable intake manifold between the air filter housing and the throttle valve actuator (M16/6).

Task
The hot film MAF sensor detects the air mass admitted to the engine and the intake air temperature, and sends the corresponding voltage signals to the ME-SFI (N3/10).

Design

Component Identification:

Furthermore the intake air temperature is detected by a further temperature resistor.

Function
The electronics in the hot film mass air flow sensor controls the temperature of the heating resistor (RH) by means of a variable voltage in such a way that its temperature is 160 °C above the intake air temperature detected by the temperature resistor (RL).
The temperature of the heating resistor (RH) is detected by the sensor resistor (RS). If a temperature change occurs as a result of increased or reduced air flow, the electronics regulates the voltage at the heating resistor (RH) until the temperature difference of 160 °C is achieved again.
This control voltage serves as a measure for the metered air mass.

The air mass is transmitted via a frequency signal (low frequency for low air mass) to the ME-SFI [ME] control unit. Using DAS, the cycle duration of the frequency signal can be read out in micro seconds.

The intake air temperature is detected by the intake air temperature sensor (B2/5b1) integrated in the hot film mass air flow sensor and sent to the ME-SFI [ME] control unit as a voltage pulse.