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Mass Air Flow Sensor Replacement
 
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Pelican Technical Article:

Mass Air Flow Sensor Replacement

Nick Czerula

Time:

1 hour1 hr

Tab:

$200

Talent:

*

Tools:

Flathead screwdriver, 10mm socket and ratchet

Applicable Models:

BMW 323Ci Coupe/Conv (1999-00)
BMW 323i Sedan/Wagon (1999-00)
BMW 325Ci Coupe/Conv (2001-06)
BMW 325i/xi Sedan/Wagon (2001-06)

Parts Required:

Mass air flow sensor, engine air filter. O-ring

Hot Tip:

Work with a cool engine. Clear engine fault codes when done

Performance Gain:

Car will run well.

Complementary Modification:

Replace engine air filter, inspect intake air ducts for cracks or dry rot.

The BMW E46 digital engine management (DME) systems use a hot-film mass airflow sensor, installed between the air filter housing and the intake manifold, to monitor air flow into the engine intake. Inside the sensor, there is a thin metal film, which is maintained at a constant temperature via electrical current from the ECM. As ambient air flows over the film, it is cooled down and additional current is needed to maintain its constant temperature. The ECM monitors this additional current to determine the mass of the incoming air and to adjust fuel supply accordingly. Note: as the temperature of ambient air increases its volume expands. Since the airflow sensor hot film monitors the temperature of the passing air, it automatically adjusts for the increased volume (= lower density) of the incoming air.

Mass air flow sensors accuracy skews over time and can lead to fault codes or drivability problems. When replacing, inspect the plastic intake air ducts for cracks or dry rot. If the intake air ducts are faulty, replace them first and see if the problem you are having is remedied. An unmetered air leak downstream of the mass airflow sensor will set codes similar to a faulty mass airflow sensor. When you suspect a mass airflow sensor as the culprit for setting a fuel trim fault code, check when the fault code was set. You can do this using OBD II freeze frame data. Normally, a vacuum leak would set a fuel trim fault code at idle or very low engine RPMs. A mass airflow meter would usually set a fault code when you are driving, or at a higher RPM. You can check your fault code freeze frame data using an OBD II scan tool, similar to how you would check for fault codes. 

In this tech article I will show you how to replace the mass airflow sensor on the BMW E46.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches. 

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you are working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability. 

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Remove the air filter housing assembly fasteners (yellow arrows) and disconnect the air flow meter electrical connector (green arrow).
Figure 1

Remove the air filter housing assembly fasteners (yellow arrows) and disconnect the air flow meter electrical connector (green arrow).

Loosen the air flow meter clamp (green arrow), then disconnect the duct from the air flow meter and remove the air filter housing from your engine compartment.
Figure 2

Loosen the air flow meter clamp (green arrow), then disconnect the duct from the air flow meter and remove the air filter housing from your engine compartment.

Place the air filter housing on a workbench and disconnect the mass air flow sensor retaining tabs on both sides of the sensor by pulling them off.
Figure 3

Place the air filter housing on a workbench and disconnect the mass air flow sensor retaining tabs on both sides of the sensor by pulling them off. Be careful not to lose the clips: they have a tendency to pop off and hide.

Pull the mass air flow sensor out of the E46 air filter housing.
Figure 4

Pull the mass air flow sensor out of the E46 air filter housing.

Check that the o-ring is in good shape and not worn or swollen.
Figure 5

Check that the o-ring is in good shape and not worn or swollen. Replace if needed (green arrow). Install the new mass air flow sensor into the air filter housing. If the o-ring gives you a hard time going in, apply a small amount of dish soap to the o-ring, it will slide right in and the soap will not damage your o-ring. Install the air filter housing into vehicle in reverse order of removal. Take vehicle for a test drive and then recheck your intake air duct connections.

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Comments and Suggestions:
Osi Comments: Hi,
i have BMW 323I year 2000,, i broke my MAF while cleaning it, now i ordered new one coming after 10 days, it shows gear signal on Board, and jumping with gear sound clicks, while shifting up or down, any side effect to the gear could appear if i drive till i replace the MAF.
thank you
November 26, 2016
  Followup from the Pelican Staff: I would try to clear the fault codes. If they won't clear and run normally, wait until you have the new sensor. - Nick at Pelican Parts  
Osi Comments: Hi ,

i was cleaning the MAF, for my BMW 323i 2000, But i broke it while cleaning, so now i am driving with Gear signal on board, the car still running good, but jumping when shifting from gear one to gear two, as well when slowing down,, i ordered new AIR MASS, QUESTION/?
is there any side effects could appear if i drive for while without MAF,?
November 26, 2016
  Followup from the Pelican Staff: I would try to clear the fault codes. If they won't clear and run normally, wait until you have the new sensor. - Nick at Pelican Parts  
jomiah Comments: I have an 02 325i BMW. I just put in a new air flow sensor and even if I unplug the maf sensor it stays idling as normal.
Any assistance as to the cause of that. Thanks
November 18, 2016
  Followup from the Pelican Staff: Normal? What are you trying to fix? What is the issue? - Nick at Pelican Parts  
tempest Comments: BMW e46 320i first start up of the day first 30 second no misfire then starts to misfire if I just drive no misfire read fault code low voltage maf replaced still same code found a small air leak the performance is better since I found an air leak on the break booster and the misfiring on first start was after the ccv and gaskrets was replaced also fuel filter fuel pump replaced I'm running out of idears the misfire can be on any cylinder if I let it sit at first start
October 26, 2016
  Followup from the Pelican Staff: If all cylinders are misfiring, look for something that can affect all cylinders. Fuel delivery, unmetered air leaks or mechanical engine timing. if it only occurred after a repair. Check if a hose or gasket was installed incorrectly. - Nick at Pelican Parts  
omega Comments: I have similar issues as Paul. Also there is a sign that shows just beside the gear signs on the dashboard. I have tried different Airflow meters but the light still shows and makes the car heavy to move. omega
September 28, 2016
  Followup from the Pelican Staff: What vehicle are you working on? What fault codes are stored? - Nick at Pelican Parts  
rex Comments: I have an E46 2000 318i i replaced the MAF with a new but theccar stil jurks when starting and when engaging in low gears too. What could be the problem?
September 19, 2016
  Followup from the Pelican Staff: Is the check engine light on or flashing when the problem is present? Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders.
- Nick at Pelican Parts
 
Jim K Comments: I have a 2000 BMW 323i e46 72k miles. eml light came on last Nov. Also started running very rough. Took to shop and after in-depth investigation, the determination was the Eng. Computer needed replaced. We replaced with new computer from BMW. Car ran fine for a few months. Now, back to eml light again and car running very rough. Back in shop and mechanic says he is getting same result again. He is still checking further as he can't understand how this could happen again. I have known mechanic for years and runs a local shop where most people take imported cars. Seems very knowledgeable and well respected. Any suggestions on what the problem could be here? As you know Eng. Computer cost from BMW is NOT cheap!! Help?
August 30, 2016
  Followup from the Pelican Staff: What fault codes are stored? EML light could also be the throttle housing or the wiring to the throttle housing. - Nick at Pelican Parts  
bmw325ci Comments: this is for almost every comment i am having the same problem two things get the alternator rebuilt and clean out ur catalytic converter!!
August 6, 2016
  Followup from the Pelican Staff: Gutting a cat will set a check engine light and cause you to fail an emission test, I would advise against. A charging system test is always a good idea. - Nick at Pelican Parts  
Martin Comments: Hi, Nick. I have a 2001 e46 318i. My car was loosing power and I changed the MAF. Power is back and fuel efficiency great, but my car now jerks and stutters in the mornings wjen its cold. Does not do it with the old MAF though. Please help.
June 27, 2016
  Followup from the Pelican Staff: You may have the wrong part. First thing confirm part numbers, if correct, clear adaptations and see if that remedies the issue. - Nick at Pelican Parts  
Paul Comments: I drive a 2002 bmw E46 automatic. It takes time to change gears especially to two, and it kicks if it goes to second gear. I thought is air flow meter and how much does it cost?
June 3, 2016
  Followup from the Pelican Staff: Sounds more like a transmission issue to me.

This could be a slip caused by low fluid or low pressure. Start by checking your fluid level. If it is OK, you may have worn parts causing a pressure drop and slip. I would have it checked before it gets much worse.
- Nick at Pelican Parts
 
Alyssa Comments: I have a 2002 BMW 325i, the car starts but once it hit 30 it chokes and turns off but I am able to turn it right back on
April 14, 2016
  Followup from the Pelican Staff: Could be an issue with the fuel pump. I would perform a fuel delivery system test. Check fuel pressure, volume and quality.
- Nick at Pelican Parts
 
Juan Comments: Hello ive got a 325 ti bmw and looking for a air flow meter second hand of new how much plz its very urgent
January 15, 2016
  Followup from the Pelican Staff: Used parts will have to come from a salvage yard. For a new one, give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Dave B Comments: Hi, i have a 2001 bmw330ci, after ive been driving for about 10 minuets & the engine is warm, but when i slow down to go round a tight corner & try to accelerate away there is no power for 2 or 3 seconds then it kicks in. can anyone help me with this.
December 30, 2015
  Followup from the Pelican Staff: Could be an issue with the fuel pump. I would perform a fuel delivery system test. Check fuel pressure, volume and quality.
- Nick at Pelican Parts
 
Jessica Comments: I have a 2001 BMW 325i. When at a stop my car drops under 500 RPMs then shuts off. After sitting for a while it will start but getting to a higher speed takes time yet again when I come to a stop it drops below 500 RPMs and shuts off. Here is what I replaced within the last couple of weeks: O2 sensors bank 1 & 2, fuel filter, spark plugs, I change my oil and filter religious too. I keep a basic schematic tool to read off of the codes and when I broke down in Houston it said something about my Mass Air Sensor so instead of looking into it I just replaced it with a new one but now my car does not go over 3,000 RPMs, however, it has not dropped below 500 RPMs and shut off. I also have to consider that I haven't ran it hot enough to where it was when it would shut off on me. I'm running out of options and any suggestions are welcomed.
December 13, 2015
  Followup from the Pelican Staff: Is the check engine light on? Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders.
- Nick at Pelican Parts
 
Mike Comments: Hi. I have a 2002 BMW 325i automatic and it suddenly began starting and then stalling. After looking to make sure the fuel pump was running, I checked for error codes and got the PO172 and 175 code, system too rich banks 1&2. I then looked for splits in the intake boot and found none. I replaced the MAFS about 8 months ago but admit it was not a quality replacement part. Today I disconnected the air filter assembly from the MAFS and closed off about half the air duct with duct tape upstream of the MAFS and it started up with a little hesitation but then ran ok, but not perfect. Could this replacement MAFS have gone bad and not tripped the MAFS code? Any other suggestions?
December 6, 2015
  Followup from the Pelican Staff: Yes, it is possible. The only way to be sure is to test the fuel control system. Use a BMW scan tool to see when the fuel trim is skewed. - Nick at Pelican Parts  
Dalton Comments: I have a 2007 bmw 328xi and as I am driving my service engine soon light will come on and my car feels like it is going to stall.. after about 5 minutes or so of driving like this with the shaking and vibrating, everything goes back to normal and the car drives totally fine again, and the service engine soon light disappears. I don't experience any issues with cold start vs warm start, and I don't have to turn the car off and back on to correct the problem.. It's happened twice now in the last week and I don't know what to do.
November 14, 2015
  Followup from the Pelican Staff: Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders.
- Nick at Pelican Parts
 
James Comments: I have a 2006 325xi. I replaced the starter several months ago. Since then the car stutters and the check engine light comes on. Hooked it up to for diagnosis and it gave me code P1415. I changed out the Mass Air Flow sensor and it still does the same thing. Where do I proceed from here. Could it be the air intake manifold? I removed it to replace the starter. Any ideas?
October 20, 2015
  Followup from the Pelican Staff: The code you have will not cause a starting issue, it is for secondary air. Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders.

- Nick at Pelican Parts
 
Christian Comments: Nick, I have a 2005 325i. The check engine light came on a while back. The generic codes came up as P0171 and P0174 both banks running lean. After the CEL light came on, I noticed I was getting a few less MPG's. I checked around for any air leaks but did not find any. I cleaned the MAF using MAF cleaner and it restored the fuel economy but the CEL stayed on. Recently though, I've noticed when coming to a stop after driving on the interstate, the car would be very slow to downshift. Basically not shifting until it reached around 500-600 rpms. When it would finally get to the 2-1 shift, it would shudder a little bit. After doing some research and seeing the effect the MAF has on the AT I figured I would get a new one. However due to some medical bills I could not spare the cash for an OEM, so I ended up getting an MTC part that I had read a few good online reviews figuring if it could last 10-12 months I'd be back on my feet and be able to get an OEM. When it arrived and I installed it, first off it cracked when I inserted the connector into it. Then when I started the car, it ran much, much worse than with the old MAF. It idled like crap and would've stalled out if I had not turned the car off within a few seconds less than 10 of letting it run. I took it off and found out I could not return the piece of crap and reinstalled the old MAF. The problem is now the car is even worse with the way it shifts. On the interstate I drive 120 total miles to and from work it's fine, including still getting around 28 mpg on the highway what I had been getting before the check engine light but around town driving is hit or miss. It seems to hold the lower gears too long. And when coming to a stop from fifth gear on the interstate it dips as low as 400 rpms before downshifting.
I'm going to get an OEM or at least a Siemens VDO {which I'm told is the OE supplier for the part} MAF. What are your thoughts? Is there anyway to reset the computer to make it forget about the MTC MAF? Any thoughts would be greatly appreciated.
October 11, 2015
  Followup from the Pelican Staff: Few notes: Do not use mass air flow cleaner on hot film sensors, it could damage them.
I would assume you are on the right track. Maybe you are getting the wrong sensor, which would cause trouble.

No reset, except for clearing fault codes, or going into the DME and performing a full adaptation reset. - Nick at Pelican Parts
 
bkl070 Comments: Any way to test the MAF sensor? My intake boot was ripped downstream; long since been replaced. SES light on when I bought car. Generic readers were giving Cam both and crank position sensors. I would not always get all three I only read OBDC a few times. Stupidly, I replaced w/o testing $100. I knew I needed a BMW scan so I figured when I got around to the SRS recall I would fork over the $135 for diag.. This is really nice, Ferman BMW of Palm Harbor FL sent a coupon for free Diag and align check that I used today. What they found:Crank and Intake Cam pos sensors bad and air mass flow sensor.I never got the MAF sensor b4. The leak was long ago fixed. I suppose I could have another. If I replace will the car recognize it? They wanted 4 hours @ $135 I think for the sensors. For a laugh they wanted to replace my front left CV boots for $700. This was the the only price quote on my copy. I looked to see that they wanted $540 labor for the sensors. They would love to do the boots not so much the sensors.
August 18, 2015
  Followup from the Pelican Staff: Yes, you can look at kg/h output verse engine RPM and load along with fuel trim and calculated load. You can also check voltage output and response to throttle. - Nick at Pelican Parts  
Fritz Comments: Hello, I have a 2004 325xi. A few weeks ago the service engine light came on and the transmission light also came on. The code said MAF so I replaced it. while I was in there I also cleaned the ICV. When I took it for a test drive the trans and MAF was ok but I got a P1500 code and the eml, brakes and traction control lights came on. I also had codes that it was running rich in bank 1 and 2. I replaced the ICV grommet, which was torn, and the "rich" codes went away but the P1500 remained as did the eml, etc... Do I have to have it reprogrammed? What else do you think could be wrong? it actually ran very well on the last test drive and even had decent power after all the lights came back on.
BTW-I also get the brake pad light from time to time.
June 25, 2015
  Followup from the Pelican Staff: With the EML light, I would assume a faulty throttle housing. - Nick at Pelican Parts  
D Comments: Hello. My Name is Derrick and i have a 2004 325i sedan. i have been having issues with it stalling and losing power while driving or idle and then after waiting anywhere between right away to 20 to 40 mins it starting again as if nothing happens. when it does this all my dashboard lights light up.
i have taking it to three different garages including a dealership and have had the ignition coils, spark plugs, alternator, and MAFS replaced. the MAFS and coils i did over the weekend thanks to you guys on the website and it drove great for two days and now is back to going limp on me as i drive. is there something im missing?
June 17, 2015
  Followup from the Pelican Staff: if all the instrument panel warning lights comes on, the loss of power may be due to a charging system issue. I would check charging system voltage and current when the problem is present. - Nick at Pelican Parts  
e90 fanatic Comments: Hi guys, I've been having problems with my 06 325i, when I am driving I feel like the car loses power for a second and then goes back to normal, and the rpms go down at little be while does that, its like something was holding me up and then letting me go, I don't know if is an transmission problem or something to do with the mass air flow sensor... The check engine hasn't come on...this is driving me crazy, I will really appreciate your help... Thanks..
April 16, 2015
  Followup from the Pelican Staff: If the MIL is off, there could be a pending code, this code will help direct you to the issue. It could be a misfire or many other items. I would start by checking for fault codes. - Nick at Pelican Parts  
riz hoque Comments: thank you nick! So you don't think replacing the MAFS will resolve the stalling issue? This issue is identical to the one Tony had. Do you know what how he fixed it?
January 5, 2015
  Followup from the Pelican Staff: It's hard to say, I am not one diagnosing.

I will note, most MAF sensors on modern BMWs cannot be cleaned. Cleaning will damage them. You didn't mention what vehicle you had, but I wanted to note this.

You will h ave to start with checking for fault codes and performing some tests to determine what is faulty.- Nick at Pelican Parts
 
Riz Comments: No The engine light is gone after cleaning the MAFS now but engine still stalls/limps after I hit the gas hard and the RPM goes more than 3000 RPM.
January 3, 2015
  Followup from the Pelican Staff: I would perform a fuel delivery system test. Check fuel pressure, volume and quality.
- Nick at Pelican Parts
 
RIz Comments: Hello Nick, I have a manual 2004 BMW 325CI and having similar issue. Every time I hit the gas hard and the RPM goes more than 3000 with fuel intake more than 10 LPM the car stalls or goes to limp mode with all warning lights on the dash board. After this happened few time my engine light came on and the fault code was P16A7 and P0171. I took it to my garage and they diagnosed it and found that my MAFS was not working properly. So they serviced it and now the engine light is gone but the stalling/limping issue is still there. I am wondering if I should replace the MAFS to fix this problem or could this be some other issue like 02 sensor, spark plug, injectors etc.
Thank you for you time.
January 3, 2015
  Followup from the Pelican Staff: Is the check engine light on? Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders. If you don't find a misfire, could be a fuel delivery issue. - Nick at Pelican Parts  
waz Comments: So, is a non-OEM MAF sensor replacement adequate? What risks in a less expensive knockoff? thx
October 8, 2014
  Followup from the Pelican Staff: I prefer better quality parts. Quality and part lifetime are sacrificed. - Nick at Pelican Parts  
Tony Comments: Hi Nick thanks for the reply, I have replaced the CCV and all lines related, DISA valve and smoke tested intake and did not find any leaks. Back pressure is with in spec. I also pulled the o2s out and road tested no change in mass air flow reading and still very under powered also what's happening is the car is going in to limp mode when applying a heavy load usually up hill in a higher gear, I have to pull over and restart so I can drive it and.......I have installed another mass air flow meter from a friends car and I still have low readings and low power issue.....this thing car is driving me NUTS!....let me know if you have any suggestions thanks again Nick!
September 3, 2013
  Followup from the Pelican Staff: Sounds like at some point you check everything. I would guess you may have missed something along the way. I would start again witht he basics, check that you have good spark at each cylinder, then confirm all the injectors are firing. Check fuel pressure, volume and quality. Then engine compression. - Nick at Pelican Parts  
tony Comments: Hi, I have a 2004 bmw 325ci, has a fault code 28a2 mass air flow implausible. I have installed new intake boots and mass air. but mass air flow readings are still well below spec. can anyone help me with this?
August 10, 2013
  Followup from the Pelican Staff: You could have another component that is faulty. It could create a low power situation (low air flow. First you should chekc that the wiring going to the sensor is good and that the signal is being sent to the DME. You might have an air leak in another component or a backpressure problem. - Nick at Pelican Parts  

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