Hot-Film Air Mass Meter (HFM)

Air volume input signal is produced electronically by the HFM which uses a heated metal film in the airflow stream. ECM relay provides the operating voltage. As airflows through HFM, the film is cooled changing the resistance which affects current flow through the circuit. The sensor produces a 1-5 volt varying signal. Based on this change the ECM monitors and regulates the amount of injected fuel. If this input is defective, a fault code will be set and Malfunction Indicator Light (MIL) will be illuminated when OBD-II criteria is achieved. ECM will operate engine using throttle position and engine RPM inputs. HFM is non-adjustable.