Mass Airflow Meter

Two types of airflow meters are used. The first is a potentiometer type (Stanza vane airflow) which uses a swinging door to measure the rate of airflow. The amount of air door movement is translated to the ECU via voltage signals. An air temperature sensor is also incorporated into this airflow meter.

The second type measures airflow by monitoring the change of electrical resistance in the circuit that dissipates heat from the hot wire located in path of incoming air. The more incoming air entering through the airflow meter, the more heat removed from the hot wire. The more heat removed from hot wire, the less resistance present in that circuit. The ECU evaluates the airflow rate through this change in resistance.

If airflow meter output voltage is less than or greater than the preprogrammed value, the ECU senses an airflow meter malfunction signal. The ECU then temporarily takes its driving condition information from the throttle position sensor. During this period of time, the ECU limits the RPM of the vehicle to a preset amount. This serves to alert the vehicle 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 cylinder head temperature is greater than 239°F (115°C).