bam_bam_dip
Veteran Member
Mass Airflow Sensor
From TDIClub
The Mass Airflow Sensor or MAF sensor is responsible for transmitting air flow data to the ECU. It is a relatively simple process. The main part of the sensor is a heating element. It is heated to a predetermined temperature. As the car runs air is drawn over this element, which has a cooling effect on it. The ECU compensates for this cooling effect by sending more current to the heating element in order to maintain the set temperature. This increase in current is measured by the ECU and is translated into how much air is moving over the sensor (and therefore going into the engine).
The actual MAF element. This one has failed, and you can see the dirt and other contaminants on it.
The element of the MAF can become contaminated by dirt and oil (from running oiled-media air filters ,the crank case vent. Unfortunately, all these little issues can lead to MAF failure as can massive water ingestion during a severe rain storm. These contaminants will either act as an insulator, or like a cooling fin. On the Bosch unit used in the mark 4 cars, this can cause the element to overheat, and become physically deformed. This will produce erroneous measurements that are sent to the ECU; generally that less air is going into the engine then is actually present. This causes the ECU to turn back fueling, to prevent smoke from the perceived lack of air.
Diagnosing a bad MAF
An under achieving MAF can cause gradually reduced performance, stumbling, jerky starts with AC running, smoky cold starts, power drop off at higher RPM, uneven power while accelerating, cars inability to hold idle when you lift off of the pedal. The MAF is on the left side of the air filter box. Unplug MAF connector by pressing the tab on the connector in and down. It should slide off easily. Test drive the vehicle.
If performance is worse than with the MAF plugged in, your problem does not lie within the sensor.
If performance is the same as when the MAF was plugged in you may have a "dying MAF". When the MAF is unplugged, the ECU uses a default setting for MAF, which is somewhat less than normal. If the car performs the same without the MAF plugged in, it is performing somewhat less than normal. However, if you have a vacuum leak, unplugging the MAF may not change your power output level. Check your vacuum lines.
If performance increases noticeably your MAF is dead. Replace it.
You can also check the state of the MAF with a scan tool, such as VAG-COM. In the engine computer pull up group 003. Here you will see fields for MAF specified and MAF actual. From 2000 RPM in 3rd gear, accelerate with the go pedal completely depressed. The reading in the actual field should track with the specified field, and should go over 800 mg/H. In reality, the “800” reading needs to be sustained and not decay. This test should be performed under WOT and under a heavy load such as running up a long hill. If it does not the sensor is bad. Replace it.
Press the tab in and down to disconnect the connector.
Possible solutions
1. Always use a high quality OEM paper air filter. This will keep contaminants off of the MAF (and out of your engine). When installing the filter take care that it is fully seated.
2. Routine inspection and cleaning of the “snow screen”.
3. If the sensor is not too far gone, sometimes it can be cleaned with good results. You can clean with contact cleaner, but do not touch the heating element with anything (fingers, cloth, etc..). Let it dry completely before reinstalling. The MAF on the newer cars cannot be successfully cleaned - - they are far too fragile and it’s simply an indicator that you should be reaching for your wallet to purchase a new one.
4. The connector can also become dirty and/or corroded leading to less than normal signal transfer. This can be remedied almost all the time by a dab of dielectric silicone grease (aka the Cage Mod). This can stabilize the signals going to the ECU, and helps to prevent future corrosion.
5. There is an updated MAF design. However, because it is so new long term reliability is still unknown at this time.
Submitted by: bam_bam_dip
Contributors: bhtooefr, compu_85, cage, paramedick, dieseldorf, whitedog, wingnut
or
http://communityhosting.net/tdiclub/index.php/Mass_Airflow_Sensor
From TDIClub
The Mass Airflow Sensor or MAF sensor is responsible for transmitting air flow data to the ECU. It is a relatively simple process. The main part of the sensor is a heating element. It is heated to a predetermined temperature. As the car runs air is drawn over this element, which has a cooling effect on it. The ECU compensates for this cooling effect by sending more current to the heating element in order to maintain the set temperature. This increase in current is measured by the ECU and is translated into how much air is moving over the sensor (and therefore going into the engine).
The actual MAF element. This one has failed, and you can see the dirt and other contaminants on it.
The element of the MAF can become contaminated by dirt and oil (from running oiled-media air filters ,the crank case vent. Unfortunately, all these little issues can lead to MAF failure as can massive water ingestion during a severe rain storm. These contaminants will either act as an insulator, or like a cooling fin. On the Bosch unit used in the mark 4 cars, this can cause the element to overheat, and become physically deformed. This will produce erroneous measurements that are sent to the ECU; generally that less air is going into the engine then is actually present. This causes the ECU to turn back fueling, to prevent smoke from the perceived lack of air.
Diagnosing a bad MAF
An under achieving MAF can cause gradually reduced performance, stumbling, jerky starts with AC running, smoky cold starts, power drop off at higher RPM, uneven power while accelerating, cars inability to hold idle when you lift off of the pedal. The MAF is on the left side of the air filter box. Unplug MAF connector by pressing the tab on the connector in and down. It should slide off easily. Test drive the vehicle.
If performance is worse than with the MAF plugged in, your problem does not lie within the sensor.
If performance is the same as when the MAF was plugged in you may have a "dying MAF". When the MAF is unplugged, the ECU uses a default setting for MAF, which is somewhat less than normal. If the car performs the same without the MAF plugged in, it is performing somewhat less than normal. However, if you have a vacuum leak, unplugging the MAF may not change your power output level. Check your vacuum lines.
If performance increases noticeably your MAF is dead. Replace it.
You can also check the state of the MAF with a scan tool, such as VAG-COM. In the engine computer pull up group 003. Here you will see fields for MAF specified and MAF actual. From 2000 RPM in 3rd gear, accelerate with the go pedal completely depressed. The reading in the actual field should track with the specified field, and should go over 800 mg/H. In reality, the “800” reading needs to be sustained and not decay. This test should be performed under WOT and under a heavy load such as running up a long hill. If it does not the sensor is bad. Replace it.
Press the tab in and down to disconnect the connector.
Possible solutions
1. Always use a high quality OEM paper air filter. This will keep contaminants off of the MAF (and out of your engine). When installing the filter take care that it is fully seated.
2. Routine inspection and cleaning of the “snow screen”.
3. If the sensor is not too far gone, sometimes it can be cleaned with good results. You can clean with contact cleaner, but do not touch the heating element with anything (fingers, cloth, etc..). Let it dry completely before reinstalling. The MAF on the newer cars cannot be successfully cleaned - - they are far too fragile and it’s simply an indicator that you should be reaching for your wallet to purchase a new one.
4. The connector can also become dirty and/or corroded leading to less than normal signal transfer. This can be remedied almost all the time by a dab of dielectric silicone grease (aka the Cage Mod). This can stabilize the signals going to the ECU, and helps to prevent future corrosion.
5. There is an updated MAF design. However, because it is so new long term reliability is still unknown at this time.
Submitted by: bam_bam_dip
Contributors: bhtooefr, compu_85, cage, paramedick, dieseldorf, whitedog, wingnut
or
http://communityhosting.net/tdiclub/index.php/Mass_Airflow_Sensor
Last edited:
