HFM/Mass Air Sensor, OEM - E46 M3, E60 M5, E63 M6, MZ3 S54, Z4M

The HFM on the E46 M3, Z3 M Roadster, Z4 M, and the E60 M5 and E63 M6 is one of the critical sensors used by the engine computer to regulate fuel injection. The HFM on the S54 and S85 measures the volume as well as the temperature of the incoming intake air. Both measurements are key for the ECU to determine how much fuel to use. Data from the HFM is also used by the ECU to adapt to different driving conditions, fuel economy, and engine condition. The ECU will not be able to adapt if the HFM is not supplying data. If the HFM goes bad a check engine light will appear, along with a number of potential fault codes (system too lean/too rich, misfires, and fuel metering, and others). This is the OEM HFM, made by Bosch, one of the suppliers to BMW for this part as well as other engine components.

S54 I6 engine uses one HFM
S85 V10 engine uses two sensors