Most people shorten the name to MAF sensor, or even further to MAFS. After 124k miles, I thought mine could probably do with a spring clean...
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Symptoms of a Faulty MAF Sensor
Some of the symptoms of a faulty, or dirty, MAF sensor are:
- the engine being difficult to start,
- stalling after starting,
- hesitation during acceleration.
If you're experiencing these problems, you might want to check and clean your EGR valve at the same time. I'd recommend bypassing the E46's EGR valve if you find yours is clogged with carbon deposits. Before taking any parts off, check the condition of the wires going into the MAF sensor connector / plug, if they've gone bad they are likely to be causing the symptoms of your fault (thanks for the tip Andy C!)
I wasn't experiencing any of the above symptoms, but by cleaning the sensor it would hopefully prevent them ever occurring, or at the very least prolong the MAF sensors life. The cost of replacing the E46 MAF sensor ranges from £20 to £60, depending on where you source the part.
You need a specific cleaner when cleaning electrical components, anything else could damage the sensor or circuitry.
After searching around for MAF sensor specific cleaners, I settled on CRC Air Sensor Clean*.
Removing the E46 330d MAF Sensor
Removing the MAF sensor on the M57 330d engine was actually quite easy, it's just a case of removing the plastic engine covers, air filter ducting and finally the MAF sensor itself. Two Allen head bolts attach the MAF sensor to the intake ducting, and two Torx head screws hold the sensor to the air filter housing. If you're struggling to get to the bottom Torx, use a flexible extension (thanks for the tip Jonny Voon).
Once these are removed, and providing the electrical connector has been unclipped, the MAF sensor unit just pulls away.
When removed you can see how much grime has built up, and surprisingly for this car, there wasn't much. There was a few small areas of dirt on the sensor but overall not bad. However, now that it was off I might as well give it a clean.
MAF Sensor Cleaning
Although this guide shows the 330d MAF sensor, the same method of cleaning can be applied to the 318d and 320d models too.
I laid out some paper towels and held the sensor unit in place over the top. I then sprayed the cleaner on liberally. You shouldn't remove the electrical elements from the plastic housing to clean them.
Despite the MAF sensor looking fairly clean, the paper towel had quite a lot of dirt on it afterwards.
I let the sensor dry completely (very important!) and then refitted it. Unfortunately I didn't get a photo of it after the clean, but it did look visually cleaner. Judging by the towel too it was a worthwhile procedure. The whole procedure used around half the can to fully clean the MAF sensor, so it's good for two goes (i.e. one can will likely last you the lifetime of your ownership).
If I notice any changes to the running of the car as a result of this clean I will update this post to describe them.
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Update:
I didn't notice any difference as a direct result of cleaning the MAF sensor, but as mine was relatively clean, wasn't displaying any of the symptoms of a faulty MAF and the fact that I'd carried out other changes at a similar time, I wasn't really expecting any difference.
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Let me know what you guys think in the comments below, have you had MAF sensor problems? Has cleaning the sensor resolved them?
15 Comments
so...did you notice any improvement?
ReplyDeleteUnfortunately, I couldn't say for definite as I had done other changes in a similar time frame. Also I don't think mine was dirty enough to make a huge difference.
DeleteIt was a peace of mind task for me really, and I suppose when combined with everything else, yes it has made a difference as the car runs much better than when I first took ownership of it.
Hi, I'm not a mechanic but decided to clean maf as car is not running well and a clean is cheaper than a new maf. Great to see your pics as its exactly the same a s mine. Does it matter which side younspay the cleaner in from? I can't see how the sensor actually cones out or does it? I can see a small little square plate thing and it looks quite dirty so hope this will help. Also did you notice oil in the small pipe under the maf? Hope this is normal,
ReplyDeleteThanks for your help
I removed the unit exactly as shown in picture three, I didn't remove the sensor from it's housing, I left well alone. I don't think it matters which direction you spray from, just make sure you clean all the relevant areas.
DeleteCan't say I remember noticing any oil, but that isn't to say there wasn't some there, unfortunately can't comment on this question I'm afraid.
Hope this helps, just remember to be careful with the MAF, as you seem to know, replacing one is expensive.
Cheers,
Andy.
Removing the MAF is a pain in my ass. I couldnt get the bottom torx screw out no matter how hard i tried, I spent an hour trying. I dont know if you have tiny hands or something. But it was not easy for me. If that screw came out happily it would have easy but the screw placement is so bad.
ReplyDeleteHi Alex,
DeleteDon't worry it wasn't just you that struggled with it, the position is somewhat unsympathetic to servicing to say the least. It's just a perseverance task more than anything unfortunately. At least you managed it in the end by the sounds of it.
Thanks for commenting,
Best regards,
Andy.
Great write up. A tip for those struggling to remove the bottom torx - I used a screwdriver with a flexible extension. Pull the duct out of the way and get in there! Unfortunately it didn't stop me from dropping the bl**dy screw when trying to put it back on!
ReplyDeleteCheers Jonny, good shout on the flexible extension would definitely make life easier.
DeleteBest regards,
Andy.
I have a running issue (hunting idle and sluggish /power loss until turbo) with my 2000 e46 330d. It could be MAF but may not be. I found EGR valve was stuck even after thorough cleaning and this was causing hunting and suspect starving the engine...reducing power, too much exhaust in intake... EGR are a flawed invention in my opinion so disconnected vacuum hose from EGR, blocked vacuum hose and EGR vacuum nozzle...car runs better, no error codes but still hunting BUT with smaller range...again only when cold...so cold routines must differ from hot routine. I could suspect ingectors or MAP sensors or turbo leak somewhere...but will clean MAF properly first...from what I have seen cleaning the small orange signal diode or spraying into outer casing is only going to through more shit into the sensor and this is not cleaning the actual sensor itself so plan to extract the MAF from housing using a cheap tool for available on ebay..(SECURITY STAR TORX KEY T-20 T-25 T20 T25 FOR MASS AIR FLOW METER 5&6 POINTS) the torx sxrews are the 5 star security torx .. so need the special torx for this.. anyway there is a video on YuTube showing how to test a MAF that increasing engine revs increases the dc Voltage output from 0 Volts to 5 Volts from the MAF sensor so its not difficult to see it working if can get to the correct pin and also understand the reverse may be true for MAP sensor - voltage decreases from 5Volts to 0 volts as air pressure increases... it does make me wonder if the MAF sensor is that critical a component if the engines run without it connected!!? I suspect it is an over rated component and may not be as significent cause of hunting unless these deteriorate but do not fail over time? - maybe people suspect this because it is at the start of the airflow chain....and easiest to get to? only way to really find out is forget about fault codes, test the sensors in position... wondering whether a clamp meter would be best for this as not interfereing with electrical connections directly...I do wonder what the diode does - normally a diode is used to prevent reverse connection but diode voltage changes with temperature and this diode is on the outer part of the sensor, anyway working systematically from one end seems better than guessing.. start from the intake and work way round sounds like a plan? would be nice to know how long BMW rates the life on these MAF sensors, do they oxidise? Do BMW have a test for them visual or electrical - for £100 a go they should have!
ReplyDeleteCheck all the vacuum lines that connect to the egr and the turbo if they seem fine you may have a problem with Pressure converters that you can open and clean them.I had the same problem with my 320d now it runs perfect after i cleaned the pressure converters.
Deletei did all the above and mine turned out to be a bad connection into the maf plug and the turbo pressure converter plug all is ok now try it because i had no fault code,but i just came across a bad wire to these plugs
Deleteall it will be is a bad connection to the maf or vac pressure converters, the plugs where the wire gos in becomes faulty,,this will save u time aqnd money
ReplyDeletei had all these common power loss faults and idle control up and down,BEFORE u go through all the might be,s check the wires going into the maf plug and the vac pressure converter plugs because them become shite and it go>s undetected,iv had this problem, people told me all the common stuff to check as i checked a few stuff i came across a bad connection to the maf plug and to the turbo boost converter plug all is fine now, it go like a rocket,,let me knw guys
ReplyDeleteI cleaned the maf and intake temp sensor en map intake pressure sensor. Went from 700km to a tank to 1000km to a tank.
ReplyDeleteAwesome result! Well worth the effort of cleaning them for those kind of gains. Thanks for the comment Johan.
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