Edito sobre los 20xe porque esto es lo que dice en el manual de las Motronic

"Hot Wire Air mass meter (AFS)
Motronic 2.5 also uses a Hot Wire airflow sensor to measure the mass of air entering engine. From the air mass, an accurate fuel
injection pulse can then be calculated. Hot Wire is a very accurate method of calculating the engine load (air input) and excludes
the need for additional sensors to measure air temperature and air pressure. Automatic compensation for altitude is thus
provided. The absence of moving parts improves reliability and lessens maintenance requirements.
Essentially, the hot wire is so called because a heated wire is placed in the air intake. As air passes over the wire it has a cooling
effect in proportion to the mass of air. As airmass increases or decreases according to engine load, the ECU adjusts the current
flow to maintain the wire at its original resistance and temperature. By measuring the change in current flow, the ECU is able to
determine the mass of air flow into the engine. As the current varies on the signal wire, so does the voltage and an indication of
load can be assessed by measuring the variable voltage signal. Voltage is applied to the sensor from the system relay.
If a fault exists in the Hot Wire AFS or wiring, an appropriate code will be logged in the self-diagnostic unit and a substitute value
provided by the LOS program."

Saludetes.