Airflow sensors are employed on engines with multiport electronic fuel injection. It is because the quantity of fuel delivered by an EFI system is managed by a computer (powertrain manage module or PCM) which turns the fuel injectors on and off. The airflow sensor keeps the computer informed about just how much air is currently being pulled in to the engine past the throttle plates. This input as well as details from other engine sensors allows the computer to calculate how much fuel is required. The computer then raises or decreases injector duration (on time) to provide the proper air/fuel ratio.

On engines outfitted with Throttle Body Injection (TBI) or maybe a Speed-Density form of EFI system (most Chryslers and some GM applications), air flow will not be measured right but is estimated applying inputs from the throttle position, manifold air temperature and manifold absolute strain (MAP) sensors. But on engines with airflow EFI systems, airflow is measured directly by a vane airflow (VAF) sensor, a mass airflow sensor, or on some Japanese applications, a “Karman-Vortex” airflow sensor.


Vane airflow sensors (also identified as airflow meters) are observed generally on German imports outfitted with Bosch L-Jetronic fuel injection, Japanese imports equipped with Nippondenso multiport electronic fuel injection (made below Bosch license), and Ford vehicles equipped with all the Bosch multiport EFI (such as Escort/Lynx, Turbo T-Bird and Mustang using the 2.3L turbo engine, Ford Probe with the 2.2L engine), and numerous other helps make and models of cars.
Vane Airflow VAF Sensor


A vane airflow sensor is found ahead in the throttle and monitors the volume of air entering the engine by way of a spring-loaded mechanical flap. The flap is pushed open by an volume that is definitely proportional to your volume of air getting into the engine. The flap includes a wiper arm that rotates against a sealed potentiometer (variable resistor or rheostat), making it possible for the sensor’s resistance and output voltage to alter in accordance with airflow. The increased the airflow, the additional the flap is forced open. This lowers the potentiometer’s resistance and raises the voltage return signal towards the computer.

The vane airflow sensor also consists of a security switch for your electric fuel pump relay. Airflow in to the engine activates the pump. So in case the engine will not start because the fuel pump will not kick in, the challenge may well be inside the airflow sensor. The easiest to examine the safety switch is usually to turn the ignition key on and push the flap open. In case the fuel pump will not come on, the contact in the sensor is in all probability defective.

A sealed idle mixture screw can also be located on the airflow sensor. This controls the quantity of air that bypasses the flap, and as a result the richness or leanness from the fuel mixture.


Vane airflow sensors along with the many other kinds of airflow sensors can not tolerate air leaks. Air leaks downstream with the sensor can make it possible for “unmetered” or “false” air to enter the engine. The more air can lean out the fuel mixture triggering a range of driveability issues, which includes lean misfire, hesitation and stumbling when accelerating, as well as a rough idle.

Dirt could also trigger troubles. Unfiltered air passing through a torn or poor fitting air filter can make it possible for dirt to create up within the flap shaft of a vane airflow sensor triggering the flap to bind or stick. The operation from the flap is usually tested by gently pushing it open having a finger. It should open and close smoothly with even resistance. If it binds or sticks, a shot of carburetor cleaner may perhaps loosen it up otherwise the sensor can have to become replaced.

Backfiring from the intake manifold can force the flap backwards violently, frequently bending or breaking the flap. Some sensors have a “backfire” valve developed to the flap to safeguard the flap in situation of the backfire by venting the explosion. But the antibackfire valve itself can become a supply of problems if it leaks. A leaky backfire valve will result in the sensor to read very low as well as engine to run wealthy.


For Bosch applications, there may be a special Bosch tester to check the output of the sensor. But a technician could also test a vane airflow sensor by making use of a multimeter to check the voltage and resistance values concerning the sensor’s various terminals.

As being a rule, the sensor’s output voltage really should rise from about 0.25 volts up to about 4.5 volts as the flap goes from closed to open. When the voltage studying is reduced, the reference voltage from the computer (VRef) need to also be checked (it ought to be 5 volts on most applications).
vane airflow VAF sensor waveform

Viewing a vane airflow sensor’s output on a digital storage oscilloscope (DSO) is often a superior strategy to detect “skips” or dead spots during the sensor’s internal potentiometer. A superb sensor really should create a smooth and gradual voltage transition from idle to broad open throttle. Changes from the sensor’s voltage output should also make a corresponding modify in fuel injector duration if the engine is running. Injector duration ought to improve since the VAF flap is pushed open.

The rheostat that senses the position on the air flap most usually becomes worn from the positioin just above idle to about 20% throttle. This really is exactly where most challenges are very likely to arise.

Vane airflow sensors are not serviceable, so must be replaced if you will find any inner problems using the unit. We???ve heard of people taking the sensor housing apart and working with electronics cleaner to clean the rheostat contacts. This may possibly restore regular operation should the contacts are usually not worn, however it will be no help in case the sensor has an electronic fault or maybe a broken flap.