Mass Airflow Meter

The mass airflow meter uses a hot-wire type sensing element. Incoming air passing through the airflow meter causes the hot wire to cool. As a result, ECU must apply additional current to maintain hot wire at the precalibrated temperature. The ECU measures airflow by monitoring the amount of additional current required to maintain hot wire at the precalibrated temperature.

On Throttle Body Injection (TBI) models, airflow meter is mounted on the side of throttle body, where it measures a small portion of incoming air. On Port Fuel Injection (PFI) models, airflow meter is located in main air intake duct.

If airflow meter output current is outside normal operational range, a malfunction in airflow meter is indicated. ECU will go to throttle position sensor for information on driving condition. During this period, ECU will limit engine speed to less than 2000 or 3000 RPM depending on model. This will inform the driver that the vehicle is driving under fail-safe conditions and needs attention.

Since the hot wire is exposed to atmospheric contaminates, the ECU is programmed to clean the hot-wire each time the ignition switch is cycled off. This is accomplished by heating the hot wire to 1832°F (1000°C) for one second after ignition has been turned off for 5 seconds. This function will not occur if engine speed has not exceeded 1500 RPM, vehicle speed has not exceeded 12 MPH, engine has stalled with ignition on, or engine is hot.