How to check the air flow sensor?


How to check the air flow sensor? (DFID)

Everyone knows that normal car engine work requires high-quality and properly prepared fuel mixture. For its formation two components are required – gasoline and air. The engine operates in various modes, and each has its own requirements for the preparation of the mixture and the volume of oxygen. Air flow sensor (DFID) controls and provides quality work of the force unit.

Main purpose

The main task of the sensor is to calculate the volume of air that is required for the preparation of the fuel mixture. The sensor must also transfer data to an electronic control unit. Then it uses the computer to increase the air flow volume or leave it unchanged. The sensor design is very simple. It consists of a plastic base and a special measuring device – an anemometer. Its mission is to conduct accurate calculations of air rate.

Common malfunctions

During its operation any sensor may get broken. As a rule, this product is most afraid of mechanical damage. In this case, it is useless to repair the sensor. The only correct solution is to replace it.

How can we get to know that the sensor has been broken? Here are some key features:

– “Check Engine” light turns on the panel.

– Disrupted power unit (especially noticeable during idling).

– The car “grows dull” in the process of acceleration and deceleration responds to pressing the gas pedal.

– Idling speed is too low or too high on the contrary.

– You cannot start the engine.

It is impossible to push all the blame on the air sensor. As practice shows, it may not work for other reasons: decompression of the hose between the throttle module and flow meter, a violation of the electrical wiring, power supply, and so on.

Checking features

Please note that it is impossible to conclude that DFID has been broken without diagnosis. As a rule, the final diagnosis can be put only after a complete unit check.

You may perform your work in several ways:

1. Turn off the air sensor. One of the easiest methods of diagnosis is to disconnect the power supply plug from DFID. In this case, the controller starts operating in the emergency mode. In this air-fuel mixture preparation you should consider the provisions of the throttle valve. In the process of checking please note that knee shaft speed must be 1500-1700 rpm. Then you should start testing your car in motion. Watch the behavior of the car. Note that some computers when disconnected from the DFID may not change rpm quantity.

2. Problems with the firmware. If you have previously posed a new program controller, then it is quite difficult to say with precisely what exactly have been updated. To check the device work a thin plate must be put under stress valve (it is desirable that its thickness was less than one millimeter). Once rpm quantity increases, just remove the insert and listen to the engine. If it is not stalled, then the problem is definitely in the system firmware.

3. Check the voltage. This checking is useful to you conventional multimeter. This method can be applied not for all DFID testing, but only for some Bosch products.

Testing is performed as follows:

– Set the tester limit at two Volts;

– Turn the ignition key (the panel should lit up, the engine start is not necessary);

– Take the meter and touch the red probe to the wire signal from the sensor, and the black probe – to ground. Please note that the connector will have a special sealing (insulation). It must be punctured by sharp probe ends;

– Record the voltage level, which a multimeter shows. The new sensor should show the parameter in the range of 0.996 to 1.01 volts. If the sensor is soon broken, the power will be closer to the mark of 1.03-1.04 volts. Thus, DFID needs to be replaced with an increase in voltage level to 1.05 volts or higher.

4. Sensor checking. As we have already mentioned, it is quite hard to assess the sensor condition after a visual inspection. However, preliminary conclusions can be drawn with the help of indirect evidence. In the process of checking you should unscrew the clamp bellows, which are connected to the DFID outlet and inspect the inside of the sensor tube. All the surfaces must be absolutely dry if the device is healthy. If there is a drop of oil or condensate, it is a malfunction of the sensor. The cause of these problems can be delayed while replacing the air filter. As a result, the dirt penetrates in a sensor mechanism. Oil may be a thrown if DFID has exceeded its level in the crankcase.

Remove the sensor (you need to unscrew the two screws) and take it off. Then find a special O-ring at the front of the unit. Its role is not to give air passing into the intake tract, bypassing the DFID. There are cases where the seal remains in the air filter or shifted from its place. If this happens, just check the air sensor grid. It should have a little dust. Therefore, you need to make sure the seal is well fastened.

5. The simplest test. The easiest way to make sure that the sensor has been broken is to ask a friend to give you a controller and install it on your car. If the above symptoms of malfunction disappear, the DFID needs to be replaced. Typically, other garage tests will not help. You can take you DFID to the workshop and test it on specialized equipment.


Every vehicle unit plays its own role in system operation. Therefore, please be careful and timely diagnose all possible malfunctions and eliminate them. Such a small but very important unit, as DFID, is not an exception.