Hot-Film Air Mass Meter (HFM)

Hot-Film Air Mass Meter (HFM): The air volume input signal is produced electronically by the HFM (1) which uses a heated metal film in the air flow stream. The HFM housing is mounted in the air inlet pipe between the air filter and the throttle valve.







As air flows through the HFM, the film is cooled changing the resistance which affects current flow (voltage drop) through the circuit. The ECM monitors this change regulating the amount of fuel injected.