Maf 101

bam_bam_dip

Veteran Member
Joined
Nov 17, 2004
Location
Belton, TX
TDI
99.5 Jetta TDI GL
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:

jrip

Veteran Member
Joined
Sep 17, 2005
Location
Fort Worth, TX
TDI
Jetta, 2000, Blue, TOTALED, Jetta, 2002, Green
I for one am grateful for this posting. I have already learned a lot. Thank you Bam Bam Dip.
 

Fortuna Wolf

Veteran Member
Joined
Apr 28, 2006
Location
Wilmington, NC
TDI
2002 Jetta TDI Auto Sedan
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...
 

TornadoRed

Top Post Dawg
Joined
Aug 3, 2003
Location
Saint Paul (ex-San Diego)
TDI
2003 Golf GL 5-spd, red; 2003 Golf GLS 5-spd, indigo blue; 2003 Jetta TDI wagon, Candy White; 2003 Jetta TDI wagon, silver
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

TDI Innovator Vendor , w/Business number
Joined
Jul 30, 2006
Location
Denton, TX
TDI
'03 Jetta TDI 780,000 miles (totaled out), 01 Audi TT 225 Quattro 230,000 Miles (runs great!), 00 Cabreetle Beetle dash, ALH & MK4 harness Swap
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

Member
Joined
Dec 27, 2003
Location
Venice, FL
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

TDIClub Enthusiast, Vendor
Joined
Jul 29, 2001
Location
Versailles, Kentucky
TDI
2015 Audi Q5 TDI, 2000 New Beetle
gotwalp said:
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
 

TornadoRed

Top Post Dawg
Joined
Aug 3, 2003
Location
Saint Paul (ex-San Diego)
TDI
2003 Golf GL 5-spd, red; 2003 Golf GLS 5-spd, indigo blue; 2003 Jetta TDI wagon, Candy White; 2003 Jetta TDI wagon, silver
gotwalp said:
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

Veteran Member
Joined
Jun 21, 2004
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.
 

spciesla

Veteran Member
Joined
Dec 31, 2002
Location
Reno, NV
TDI
Not any more
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

Veteran Member
Joined
Nov 17, 2004
Location
Belton, TX
TDI
99.5 Jetta TDI GL
spciesla said:
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.

 

MikeS_18

Top Post Dawg
Joined
Feb 18, 2005
Location
Bow, NH
TDI
'03 Jetta Wagon, '13 Passat SE, '64 Ford Econoline
I took the whole assembly out and took a dremel to the screws and made them into slotted screwdriver screws. Piece 'o cake!
 

cbass94

Veteran Member
Joined
Jun 14, 2006
Location
Salt Lake City, UT
TDI
2003 Jetta GLS, 2011 JSW
Can someone look at the post in the link below and tell me if the MAF readings are good? I am helping a friend diagnose his Golf and I don't have much experience with TDI's (although I am frantically looking for a good one I can afford) because I have an Audi and they're stupid for not bringing their TDI's over here. To me the MAF readings look good, but the boost readings look like they're struggling. If someone can confirm that the MAF readings are good, I'll be on my way to search for a boost leak and won't hijack the thread anymore.

http://forums.tdiclub.com/showthread.php?t=118116

BTW, great post about the MAF sensor, I learned a lot! Thanks.
 

bam_bam_dip

Veteran Member
Joined
Nov 17, 2004
Location
Belton, TX
TDI
99.5 Jetta TDI GL
I'm no vag-com expert, but appears that your maf has defaulted to the "default" settings.

Try unplugging and do the red line test. 5100 rpms indicates a good maf, less than that would lead me to believe that maf is bad.

next, try unplugging and go for a test drive. Did the performance decrease, increase, or was it similar to having the maf plugged in???
 

F-18 Rep

New member
Joined
Sep 12, 2006
Location
St Louis
TDI
06 Jetta
My 06 Jetta TDI seems to be a little low on power. Big rain storms here this summer may have contributed to a failing MAF. I know it is covered under warranty but hesitant to trust the dealer, so thinking I might do the test suggested above (disconnect MAF) before taking it in. Question: won't this set an engine code and or a check engine light? Also, will replacing the tamper-proof screws result in warranty problems? Suggestions welcome.
Thanks, Bruce
 

Butane

Well-known member
Joined
Sep 12, 2006
Location
Green Bay, WI
TDI
2003 Golf GLS TDI
as far as the tamper proof screws, grand rapids industrial products (GRIP) makes a very inexpensive set of torx wrenches that have both the regular heads and the security heads like these screws...
 

sk8rdi16

Veteran Member
Joined
Jul 8, 2006
Location
Long Beach, Mississippi
TDI
'05 Golf
Quick question about the MAF. Mine was dying, so I replaced the entire body with a new one from TDIparts. When I first started up after installing, my Golf studdered and shuddered badly, with tons of smoke! Is it possible it is a bad MAF? I remember reading somewhere that it takes the ECU a while to learn the new signal, but I couldn't find it anywhere. It smokes on each cold start now as well.
 

nicklockard

Torque Dorque
Joined
Aug 15, 2004
Location
Arizona
TDI
SOLD 2010 Touareg Tdi w/factory Tow PCKG
Occasionally a MAF can partially fail such that you might have 'holes' in the power band. In this case, unplugging the MAF will tell you nothing, and you will be forced to swap your suspect MAF for a friend's known-good MAF to diagnose further. I know of no alternate way around this.

{It happened to me.}
 

khb137

Member
Joined
Mar 25, 2005
TDI
1999 jetta silver
Maf ?

Does the MAF have a Given life spane of working and working not so well
and shoud just be replace when cleaning does not help

:eek:

1999 Jetta 169,000
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
Should be replaced when it fails. Some last 200,000 miles, some 1,000.
 

celry

Well-known member
Joined
Jul 6, 2004
Location
Washington DC
TDI
2001 Jetta auto; 2011 JSW dsg
power loss / MAF diagnostic - next step

So my 2001 Jetta ALH auto GLS has had a loss of power recently, but only at about 1.5 hours into roadtrips.
Symptoms are:
At highway cruising speed 60-75 mph, and on distinct uphill climbs, it gets to about 2200rpm, no more. Starting at 75, heading up a hill, throttle floored, RPM's constant, speed decreases to 50-55 until the following downhill, where I get back to 75 slowly but without umph.
This only happens after at least an hour on the road. City (short trip) hills are no problem at all.

I got to this thread by searching power loss etc, and I'm guessing the problem is the MAF. Or is it a clogged EGR? Or something else?
I am loath to buy the new $115 part (tdiparts.com) without more clear sense that this will fix the problem.

Diagnostic so far:
I've unplugged the MAF and boy those contacts look shiny and clean.
No bubbles in the fuel filter line.
No apparent relationship to weather - it's been 70F, it's been 20F too.
I change all the filters per the VW maintenance schedule.

How does this sound as the next step?
I have a roadtrip planned for West Virginia (mountains) this weekend. I fully expect to have the power problem. At that point, I unplug the MAF and see what happens. IF I understand previous posts, IF the MAF is bad the power will be fine with the MAF unplugged? Would leaving it unplugged for the duration of the trip do any damage other than increase fuel consumption?

Thanks in advance for any insight/ advice.
 

bam_bam_dip

Veteran Member
Joined
Nov 17, 2004
Location
Belton, TX
TDI
99.5 Jetta TDI GL
celry said:
So my 2001 Jetta ALH auto GLS has had a loss of power recently, but only at about 1.5 hours into roadtrips.
Symptoms are:
At highway cruising speed 60-75 mph, and on distinct uphill climbs, it gets to about 2200rpm, no more. Starting at 75, heading up a hill, throttle floored, RPM's constant, speed decreases to 50-55 until the following downhill, where I get back to 75 slowly but without umph.
This only happens after at least an hour on the road. City (short trip) hills are no problem at all.

I got to this thread by searching power loss etc, and I'm guessing the problem is the MAF. Or is it a clogged EGR? Or something else?
I am loath to buy the new $115 part (tdiparts.com) without more clear sense that this will fix the problem.

Diagnostic so far:
I've unplugged the MAF and boy those contacts look shiny and clean.
No bubbles in the fuel filter line.
No apparent relationship to weather - it's been 70F, it's been 20F too.
I change all the filters per the VW maintenance schedule.

How does this sound as the next step?
I have a roadtrip planned for West Virginia (mountains) this weekend. I fully expect to have the power problem. At that point, I unplug the MAF and see what happens. IF I understand previous posts, IF the MAF is bad the power will be fine with the MAF unplugged? Would leaving it unplugged for the duration of the trip do any damage other than increase fuel consumption?

Thanks in advance for any insight/ advice.
It may well be the MAF, but it sounds more like your car is going into limp mode. You need to do some logging with vag-com, then start a fresh thread with your problems in the 101 section.
You can unplug the maf at any time and check per the requirements above.
Next time your car goes into this severe power loss, try pulling over and cycling the key off for a second and then start it back up. If you're going into limp mode, this will "reset" the ecu and the problem will go away (not permanently).
But definately find somebody with vag-com right away. If your car is going into limp mode, it is doing so for a reason the requires immediate attention.
 

nicklockard

Torque Dorque
Joined
Aug 15, 2004
Location
Arizona
TDI
SOLD 2010 Touareg Tdi w/factory Tow PCKG
Also, a good MAF will let the car rev right up to the rev limiter at 5150 rpm's while a bad MAF will not let the car rev above 4500 rpm's according to Drivbiwire. In neutral and with a warm engine, floor the accelerator and see what rpm's it attains. This will not hurt the engine at all.
 

celry

Well-known member
Joined
Jul 6, 2004
Location
Washington DC
TDI
2001 Jetta auto; 2011 JSW dsg
Wow. Ok, I'll look into finding someone with vag-com. Thanks for the immediate reply!
 
Top