Maf 101

bam_bam_dip · August 17th, 2006, 11:54

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/...Airflow_Sensor

jrip · August 17th, 2006, 21:31

I for one am grateful for this posting. I have already learned a lot. Thank you Bam Bam Dip.

Fortuna Wolf · August 17th, 2006, 23:19

Diagnosing a faulty connection can be made by unplugging and plugging the connector. Reseat the connector and see if power returns. If it does, then the remedy is the cage mod.

Perhaps not recommendable, BTW, but if you don't feel like getting silicone dielectric, vaseline or another petroleum jelly will work. Even brake grease...

X_Railroader · August 18th, 2006, 17:44

A great read and I learned something too

Thanx for the post

TornadoRed · August 19th, 2006, 21:32

Besides unplugging the MAF sensor, to see if the engine runs better, worse, or the same, I have read that there is another quick-and-dirty test. Just see if your engine will rev to 5000 rpm in neutral.

It is safe to do this. Perhaps someone else will confirm whether it is an effective test.

alphaseinor · August 19th, 2006, 22:13

I used to clean my MAF sensors with Non-Clorine based Brake cleaner... Not sure if this is the "hot wire" type or not... so... YMMV

If this is the foil type, and you have tried the Cage Mod, and it still doesn't work right, then you should at least give it a shot... can't hurt anything... or can it?

gotwalp · August 28th, 2006, 09:52

My 2000 TDI was acting real slow to go. I read this and unplugged the MAS sensor and it is a huge difference. A few questions....
Is it bad to leave it unplugged until I can remedy the problem?
Is there a way to clean the old one?
Where is the best place to buy a new one if needed?
Thanks in advance.
-Walt

paramedick · August 28th, 2006, 10:36

Quote:

Originally Posted by gotwalp

Is it bad to leave it unplugged until I can remedy the problem?
Is there a way to clean the old one?
Where is the best place to buy a new one if needed?
Thanks in advance.
-Walt

Short term, no.
No, it's toast
tdiparts.com, dieselgeek.com, worldimpex.com
You're welcome

gotwalp · August 28th, 2006, 11:42

Thanks so much. I ordered the new part from tdiparts.com
Cheers,
Walt

TornadoRed · August 28th, 2006, 18:50

Quote:

Originally Posted by gotwalp

Is it bad to leave it unplugged until I can remedy the problem?

One fellow reported that back in the days when replacement MAF sensors were very expensive (~$300), he left his defective one disconnected for nearly a full year. His TDI was chipped, so even with reduced power it was still adequate for his needs. Not sure whether it affected his fuel economy.

vegegolf · August 29th, 2006, 05:44

Assuming you take the above mentioned precautions, how long can one expect their MAF to last?

I replaced my MAF a year ago and I'm wondering if it's starting to go already.

MikeS_18 · August 29th, 2006, 06:06

http://www.crcindustries.com/auto/co...x?S=Y&PN=05110

I got some at PEP Boys.

Fortuna Wolf · August 29th, 2006, 21:57

I've never replaced my MAF. I'd say that at 88k miles and 5 years its original. Just keep it clean.

spciesla · September 6th, 2006, 19:40

I got my replacement MAF today from TDIParts.com.

Should I replace the whole thing (sensor + body) or just pull the sensor (I have the necessary security torx)?

Thanks!
Steve

bam_bam_dip · September 6th, 2006, 20:13

Quote:

Originally Posted by spciesla

I got my replacement MAF today from TDIParts.com.

Should I replace the whole thing (sensor + body) or just pull the sensor (I have the necessary security torx)?

Thanks!
Steve

I just replaced the sensor..........and replaced those silly security screws with drywall screws. Makes for easier access later.