[PhaseP]

This is a post of sharing my experience with a difficult to diagnose stubborn "system too rich" and occasional "Mass or Volume Air flow too high" codes being thrown with SES light and idle and some drivelability problems. After long trial and error and some testing and research I am confident I found the root cause and wanted to share since I saw other old posts with same problems with no conclusions to solutions from other people.

Some disclaimers: I am not a trained mechanic. What I am writing here is my own experience and I can't give any guarantees what I describe and explain is correct information or the right and safe way to work or do to a car. If you decide to use what I describe here, use your own judgement, safety, consult BMW shop manuals or trained mechanics. I am only sharing my experience with no claim that what I describe here is safe or correct way of working on the car.

Summary for TLDR people: MAF sensor connector was not making solid good connection due to too may connect disconnect cycles over 10 year service the life of the car and also due to what I believe too thin connector pins on the MAF sensor side for the connector pins used.

To start the long story, I have a first year (2006) US N52 (325XI) with a certain MAF sensor part number: 13627520519. Yours may be using different part number MAF. For instance 328 N52's are using different part number MAF even though the MAF from outside looks very much same physically and could be prone to same problem.

These were the symptoms I was having:

- Fault Code thrown: 2A2E Mixture too rich (OBD version: P0172 System too rich bank 1 )
- Fault Code thrown: 2A2F Mixture too rich (OBD version: P0175 System too rich bank 2 )
- Fault Code thrown: 2D06 value HFM to high (OBD version: P1424 Mass or Volume Air Flow Too High)
- Of course the SES light was on because of above codes
- On cold start up engine rpm was most often shooting up to between 2.5K and 3K rpm, then quickly going down.
- At warm engine idle, RPM needle was usually very close to 500 rpm mark or on the 500 rpm mark
- On idle, engine RPM was intermittently dipping, to the point of almost engine shutting down, but was recovering immediately.
- Sometimes idle RPM wasn't settling at all after coming to a stop. Normally it should have settled down to somewhere around 650 rpm after one or two seconds coming to full stop. But instead it was going down slow by slow and then up a bit and down a bit as if the engine was nervous and couldn't decide what to do.
- Car was usually feeling anemic at low rpms. Certain times it was becoming difficult to take off without stalling the engine (I have manual transmission), because even I was depressing the gas pedal it was as if something was reducing gas pedal input.
- Then a few seconds later if I had managed to take off without stalling, suddenly the anemic condition of engine was going away and I would feel this as a sudden forward thrust as engine all of a sudden was back to full power. This was happening not only during take off but also during low rpm driving, below 2K rpm. It was feeling like car had lost its mind and was not really following my gas pedal input at low rpms.
- But then some days, it had no issues. It was as if fixed itself. But only a few days later back to crazy idle rpms.
- There were no other fault codes related to these, only those three. And initially for a few months it was only the two too rich codes. 2D06 came a few months later, which turned out to be critical for me determining (or deciding ) the root cause of it.
- The freeze frame of the codes were showing short term fuel trim levels of negative 20% or so, don't remember well. This would explain the anemic condition of the engine it was not really getting too much fuel. The trim level means from my understanding, the car computer is adjusting (trimming) the amount of fuel it allows into the engine by that percentage than the ideal air to fuel ratio based on several sensor inputs as compensation, thinking it has really too much fuel to the amount of air going into the engine.

Eventually I believe I zoomed in on the real culprit and fixed this problem for good. The problem was being caused by the MAF connector wasn't making solid enough connection with the MAF sensor and resulting in intermittent disconnection of the MAF sensor from the computer. This was throwing off the computer, it was sometimes getting good value from the MAF, sometimes no (bad) value.

I had tried to clean the electrical connection pins on the MAF sensor and the cable side connector in the past as potential problem but it wasn't enough apparently. This time I ordered the parts to replace the connector, which are for my car:
P/N 12527516864 the connector housing
P/N 12527535589 rubber grommet for locking the cable loom to the connector housing
P/N 12527532371 x 5, the connection pins
P/N 61138366247 x 5, rubber grommet (seal) on the connection pins

My initial intention was to remove the connector and the connection pins and replace everything new. But I ended up replacing the connector housing and the locking grommet on the cable loom for the connector, because I decided to give a chance to cleaning the pins rather than replacing. Replacing would mean cutting them off and that would shorten the cable.

I used CAIG DeoxIt contact cleaner/conditioner which I had for electronics work. I am not sure if it is good to use it on auto connections due to the environment day live in, but on home electronics DeoxIT does clean up connectors very good. I also uses CRC QD electronic cleaner. The former removes oxidation, the later cleans up oil and dirt from my experience.

Below are steps with pictures coming next:

- Disconnected the battery negative connector on the trunk from the post and placed a paper between it and battery the post as isolation. I would be removing the connector pins and they would be touching each other, didn't want to cause any shorts or problems, so disconnected battery which was a requirement I think. (Don't close the trunk door after disconnection battery if you have one of those years that don't have a trunk manual lock, you won't be able to open the trunk with battery disconnected, just don't close the trunk )
- Then removed the connector from the MAF by lifting up the locking tab with a thin screw driver
- Removed the bottom part that locks the cable loom to the connector by prying up the two locking tabs. One got broken but I had bought new replacement.
- Jotted down the orientation of the connector and the wire colors going into it, so that I would be able to put them back at the same spots correctly.
- Pried open the middle section of the connector that locks the pins down.
- Pushed a paper clip on the top of the pins which pushed down the top spring tabs on them.
- Pulled down the wire for that pin to remove from the connector housing.
- Once all were out, I cleaned them first with the CRC Electronic cleaner. After that dried I sprayed inside of each connector pin with DeoxIt.
- I pushed the pins with the wires to the NEW replacement connector housing I had bought at the correct orientatio and order as before. Made sure they were pushed all the way in.
- Locked them in by pushing in the middle section of the connector housing, placed the loom locking bottom part.
- Cleaned the MAF connector side first with Deoxit and then CRC Electronic cleaner. I chose this opposite on the sensor since... my way of thinking.
- Pushed the new connector body to the sensor. It was much more solid in its place, hence it was important to use a new connector body.
- Reconnected the battery.
- Started up the car, and since then it has been all good. It has over a week now, SES light went off by itself, no idle issues, no erratic behavior. Simple fix!
- As usual after disconnecting battery I had to turn the steering wheel all the way side to side to get rid of the 4x4 error on the dash (an xi thing), and reset the time.

[PhaseP]

Here are pictures that would go with the steps above mentioned:







This is the final with new connector housing body, note new one has blue color:

[PhaseP]

Even though the fix was simple, coming to this resolution was not without frustration nor cheap. This is my story getting up to this piont:

First cleaned the MAF sensor, didn't work. I had cleaned the connection too but not good enough apparently. I checked coils, spark plugs, nothing bad looking. Checked vanos selenoids, they were clean as a whistle. I replaced the Oil Separator Valve and lines, car had started to use oil with no oil leaks and was thinking this may be adding oil and unburned fuel back to intake too much causing rich condition. It stopped the oil use, but not the too rich condition and erratic engine behavior. I replaced the thermostat, it was not working had its own code, I was thinking and hoping engine not reaching full temperature was throwing off computer air fuel ratio calculations. It was winter and I verified engine was never reaching full working temperature with hidden dash computer menu with the thermostat stuck open. Engine started reaching full temperature after replacement, but it didn't fix the problem. Then I replaced injectors with OEM (not cheap) after measuring it was not holding fuel pressure after shut down thinking they may have slow leak and causing rich condition. And as you guessed didn't do a thing to fix the problem. I replaced the fuel pressure regulator/filter thinking it may not be working well ending up causing rich condition, again no dice, though car ended up starting quicker, it was probably now was holding fuel pressure after shut off. Then I replaced throttle body assembly out of desperation, maybe it was acting up even though it is supposed to only work on idle, but major problem was idle. Of course didn't fix the problem. I replaced MAP sensor (had squished it from top one time but seemed to be working) just to get it off the potential list. I replaced engine coolant temparature sensor, raditor coolant temperature sensor, thinking wrong temparature readings maybe throwing off the computer's air fuel ratio mapping, and they were cheap.
None of them reall fixed it. Worse part, after most of these, the car was running fine for a week making me think I had finally fixed it, but then again after a week it was starting to act up again. It had been frustrating.

Then I started having 2D06 "value HFM to high" code too, in addition to too rich codes. The "to high" typo is not mine, it is from INPA. I found out HFM is short for Hot film meter, which is another name for the version of MAF sensor used in these cars. This code along with my experience of each time I worked on the car which resulted in disconnecting and connecting, i.e. reseating that connecter it was working fine for a week, eventually led me to suspect the electrical connection of the MAF sensor, and I do believe that is really the real culprit.
If again I get the same problem, hope not, next I will solder the wires directly to the MAF and try that!

[vautrain]

I noticed in your last photo, the screw visible on the fender side of your MAF appears rusty. Is that the case? Maybe a clue as to why your connection was wonky. I'm pretty sure mine are black or dark grey, not a spot of rust to be seen.

The engine issues you experienced were way more extreme than anything I've experienced. It's really just low MPG, and the idle dip, which only seems to occur in R, D and DS, and only after the engine is warm. And the idle would dip from about 600-650 (normal idle?) to 500 RPM, quickly, and then jump back up to 600-650. It was definitely not dipping below 500 RPM at any time, but it was a sudden enough thing to jolt the car a bit.

All this isn't to say I'm not also experiencing a connection issue, just to point out that your situation seemed much more extreme.

[PhaseP]

It is surface rust on the screw and been that way for years and years. It is a New England car. I had idle and other issues only starting this winter, and yes it got progressively worse and worse. I only try to help. It is not much different and difficult to try to clean the connector than cleaning the MAF sensor, very easy and cheap to rule out a potential culprit. My car is running fine over three weeks now, with that rusty screw still on there good luck to you !

[fravel]

Thanks for sharing! I've been battling with 2A2E and 2A2F codes for awhile and I've also spent a fair amount of money on parts with no resolution. My car still drives great so I've more or less ignored that light for awhile, but this is so cheap I gotta try it.

[PhaseP]

You have a '06 car too, which has analog output MAF like mine. So you may be having same issue, which would be easy fix. Would appreciate if you update here the result.

[fravel]

PhaseP, I gotta hand it to you, I believe this fixed my problem. Finally got the opportunity to get in and swap that connector out this past week, driven ~300 miles since and my check engine light hasn't returned.

I'm hesitant to call it "solved" just yet as I've chased this SES light for 18 months and have spent A LOT of money on parts and diagnostics only to have the SES light return shortly after whatever change, so I probably won't trust it until I get a few thousand miles in. But as you noted, I am driving an '06 vehicle and in addition I have done a fair amount of airbox modifications resulting in increased frequency of connecting/disconnecting that housing, so your hypothesis certainly fits my scenario... I'm hopeful.

Thank you so much for sharing this information, I never would have figured it out on my own.

[PhaseP]

Glad I could be helpful out of a frustrating situation. Hopefully though. Give it another week or two.
You will probably start to notice a much more peppy and powerful engine, but it may take a week or so driving for the engine to readjust the lamba adaptation values. If you have INPA setup you can reset the lamba adaptations without waiting.

[fravel]

I'm gonna go ahead and call it fixed, this was definitely the culprit. Car has been running strong and I haven't see a check engine light this year.

Thanks again!

EDIT: Honestly, this thread should probably be sticky'd. N52's with fuel mixture codes are horribly expensive to diagnose and this should really be the first "part swap" anyone tries considering how cheap and easy it is.

[PhaseP]

Again glad to be of help.

I think this is more of a problem with the '06 magnesium valve cover N52's. These have analog output MAF sensors. Later years with plastic valve cover N52's use digital output MAF sensor, those wouldn't have low voltage low current at the connection.

[PhaceN52]

Thank you, thank you and again thank you for this discover. My scenario also fits well what you've described, lots of diys so a lot of connections/disconnections on the maf... The car ('06 325i US, magnesium vc ) had trown 2D06 code only once or twice and no rich codes at all, but the hesitation at takeoff is def noticeable, sometimes it seems like the engine is going to stall... other days it seems perfect. I tried reseating the connector as you said and works like a charm, it's like a 20hp gain every time, but I'm tired to open the hood every 2-3 days just for moving that damn thing, even if I LOVE cherishing this N52..... Oil separator, plugs, coils, solenoids, gaskets, atf and who remember what else were all replaced during the last 1.5 years, "healing" the situation but not completely fixing it, so I hope this will be a permanent fix. I'll update in some weeks..
Have a nice day to all E90posters

[E90joee]

This is exactly whats been happening to my 07 328 but mines automatic so sometimes it does shutoff and it happens more when im driving more aggresive on the highway and its reving more but i also have a AA tune and headers i wonder if this will help

[Chamberlin]

Hey guys, great thread and I feel your pain... It is really nice when people take the time to properly document what happened, and all the BS they go through to get to the eventual solution.

I'm trying to help out with my dad's 2007 X3, which has the N52K (build sheet) N52N (RealOEM) engine (same as my '07 E91 wagon)... He's got all the same symptoms and his car is due for emissions this month...which can't happen with an SES light on obviously...

How can I tell if his car has the digital or analog MAF sensor? Something about magnesium valve cover?

I will try to smoke test the engine and check for vacuum leaks, but I definitely want to pursue this avenue too, as it seems the previous owner replaced the MAF sensor already, not knowing that it could have been the connector all along...

BTW, I've got the Schwaben scan tool and he's got Map Thermostat Activation code 2EF7 & Air-mass System code 2D06 that keep coming back, and then after a day or so, the 29E1 Mixture Control 2 29E0 Mixture Control flags kick in too.

T.I.A.

[PhaseP]

If your engine has plastic valve cover (black vanity cover outside) it should have digital output MAF sensor. N52K in BMW lingo I believe is the new generation N52, with plastic valve cover and etc including digital output MAF sensor.
You also have lean codes, not rich codes. I would search for vacuum leaks. You probably don't have this particular issue.
A simple test is to reseat the MAF connector and if it removes the symptoms for a few days then connector may be suspect.
Thermostat code is most probably not related. If the car is on original thermostat it is not unexpected for it to fail at that age.

[Chamberlin]

Thanks so much for your fast reply - sorry I didn't make the correlation between the rich vs. lean codes myself... I was probably subconsciously hoping it was an electrical connection problem and not a vacuum leak problem! I think we will just have to have the car smoked at our local indy shop to save time... I happen to have a new spare OEM thermostat for my E91 laying around too, probably a good opportunity to have my dad's coolant flushed and the T-stat changed out (I saw hints of nasty green coolant in his system, so you know what that means....previous owner visits Pep Boys/Grease Monkey/WalMart oil change centers).

I ordered the blue connector portion of the MAF connector last night anyways, but it looks like I probably won't need to re-build the connector.

Thanks again.

[Volasko]

I don't have ANY of the above symptoms, car still pulls strong, no misfires, good MPG, idles perfectly still at 650 BUT I'm still getting 2A2E and 2A2F codes, nothing else. Could a loose connector be the cause of my problems? The 2D06 code seems to me the main code my car would throw if the connection was intermittent with other issues following. I'm willing to try anything at this point but just wanted to ask.

Follow up:

The connector was the cause of my problems too. Holy crap what a journey that was to get to the bottom of my issues. HUGE props to PhaseP for figuring this out!

[PhaseP]

The new connector sits tighter in there. Plus during replacement since the pins are out it gives opportunity to clean them better with contact cleaner spray. Main problem I think the pins on Maf are too thin for connector side pins to grab tight enough. Any surface corrosion or dirt on the pins can throw it off. That is my theory

[PhaseP]

After you pry open the middle section flap, you push the paper clip on the hole at the top of the pins which pushes down the spring tabs. Then you pull out the wire. They should come easily. They have sealing silicon collars on them, that may give some friction resistance but not too much.
Look at the pictures I have posted.
From what I remember pushing them back into their holes required some force due to the silicon collars again. But not too much. If it is requiring too much force spring tab is still locked.

[PhaseP]

It seems not very difficult to replace that hose, with the exception of reaching the clamp on the thermostat side. That is tight in there.
You need to drain the coolant first, remove the hose (two bolts on engine block end, and a regular clamp with worm drive bolt on thermostat), refill coolant, then do bleed procedure.
If you search water pump replacement DiYs you will find a lot of information on thermostat side of that hose and drain, fill and bleed procedure of coolant.
Good luck!
Something like this with flexible shaft
https://www.amazon.com/Ideal-Tridon-.../dp/B00529CVS8
or this
http://www.oreillyauto.com/site/c/de...0741&ppt=C0195
may come handy undoing the hose clamp on thermostat side.

[xxdarkdragonxx]

Hey Everyone, Just wanted to comment on this post, I believe PhaseP has helped solve my issues with this fix. I also drive an 06 E90.
I have an 06 330i, I got the car used, and started working on it last year.

here is a summary of engine parts I have replaced:

All Coils,
All Plugs (3 times)
Disa Valves (Both of them)
MAF Sensor
both Vanos Solenoids (3 times)
Both Cam sensors
all Fuel injectors
eccentric shaft sensor (all gaskets with this job also, intake, valve cover etc)
Crank Position Sensor

a lot of parts I know! the car would sometimes run perfectly fine, then all of the sudden , it would surge, or rough idle sometimes It would for some reason after a long highway drive, drive really rough almost stall out but never did.
I would clear the codes, and reset all the adaptations, car would be fine for abit. but after 2 weeks at most it would always always act up.

I ordered the socket sensor(s) parts for the MAF and the Intake cam sensor (more on the intake cam sensor later) and did the change tonight, and the car is running extremely smooth, the idle is smoother than its ever been.

was always chasing the codes mentioned in the OP about air fuel mixture. (2A2E & 2A2F)
wasnt until a new code came up about the MAF hot film
(2D06) that lead me here. I was also chasing the Intake cam sensor signal fault (2AA0) did the same procedure on replacing the cam sensor socket, as when I would move the wires around when the car was running, instantly the car would smooth out.

when I did change out the cam sensor socket it was clear it was the problem, as soon as i started to open the socket, it fell apart in multiple pieces. cleaned all 3 terminals and took the sensor out and cleaned the pins on it as well. reinstalled everything.

loaded up inpa, cleared all codes and also reset all adaptations.
started the car and bam it was very immediate the car was silky smooth. took the car for a spirited test run on the highway, and she pulls very strong and smooth now.

time will tell if this is the ultimate fix, I am confident it is. thank you very much for sharing your experiences with all of us. Hopefully my addition of someone chasing that 2AA0 code and have replaced the cam sensor but still having issues can try replacing the sensor socket before going too deep into more things will help as well.

will post an update as to how things are running.

[Phil325i]

Useful post dragon, thanks. Which engine do you have and where exactly is the intake cam sensor located?