Air Flow Meter/Sensor: Description and Operation

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

Component Identification:

Location
The hot film MAF sensors are located at the outlet on the cover of the air filter housing concerned.

Task
The hot film MAF sensors (HFM) measure the air mass delivered to the engine.

Design
Hot film MAF sensors consist of a temperature-controlled resistor and a plastic housing with integrated electronics and a 4-pin plug connection.

Function
The integral electronics in the hot film MAF sensor controls the nominal temperature (of about 160 °C) of the heating resistor. The temperature of the heating resistor is detected via a sensor resistor. If a temperature change occurs as a result of an increased or reduced air flow, the electronics correct the voltage at the heating resistor until the specified temperature is achieved again. The control current is evaluated by the hot film MAF sensor and converted to a sensor signal (frequency signal).
The air mass is sent in the form of a frequency signal (low frequency for small air mass) to the ME-SFI control unit (N3/10). Using DAS, the cycle duration of the frequency signal can be read out in micro seconds.

Air mass Frequency Cycle duration
0 kg/hour 1890 Hz 529 micro S
150 kg/hour 3080 Hz 324 micro S
300 kg/hour 4080 Hz 245 micro S
450 kg/hour 6000 Hz 166 micro S
600 kg/hour 7010 Hz 142 micro S

The intake air temperature is also measured by the hot film MAF sensor, but not evaluated by the ME-SFI control unit. The signal from the intake air temperature sensor (B17) is used for the intake air temperature.