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  1. #1
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    Fault codes P0171 and P0174

    P0171 (227) - fuel trim bank 1
    P0174 (228) - fuel trim bank 2

    SES light came on and got the above fault codes from Autozone. Brought to independent BMW shop and confirmed the error codes 227/228. BMW tech think it's a vacuum leak somewhere but he could not find anything obvious. So he reset the SES and told me to come back if there are problems. I will spray the hoses with carb cleaner or wd 40 to detect vacuum leak but anybody has similar problems or thoughts? I know this is a common error code if you have cold air intake but I don't have CAI. Thanks in advance!
    car is E46 2002, 90K miles with new plugs, filters etc and car is running fine. Also, always use 93 octane gas.


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    For what it's worth Bentley calls these two

    codes "fuel control" instead of trim, but it doesn't even explain what this means? How are we supposed to figure this out?

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    Could be due to a dirty MAF

    Had similar fuel trim (running lean) error codes on a BMW V8 along with surging when accelerating. Cleaning the MAF solved both problems. I used CRC # 05110 Mass Air Flowmeter cleaner.

    YMMV

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    Re: Could be due to a dirty MAF

    I think you are probably correct. I just sprayed WD40 on all the vacuum lines and I could not find any leaks. But how do you clean the MAF? Do you just spray that cleaner into the throttle body and allow it to dry?? It looks somewhat tight to get access to all those air intake covers.

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    Re: For what it's worth Bentley calls these two

    The BMW tech said it is important to intepret the codes correctly. He said it's usually a torn rubber boot near the throttle body but he didn't see that in my car. It's definitely not the oxygen sensors which has a specific fault code. I will try cleaning the air intake first like KeithS says above. Thanks!

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    You need to remove the actual element (m)

    My experience is on a 540. It is necessary to remove the sensor itself from the housing to clean it properly. For the 540 I had to use a torx 20 security bit to get it out. Just follow the directions on the can for cleaning. Make sure it's good and dry before renergizing it (have heard stories of them burning out if wet).

    I've seen the CRC cleaner at Strauss and Pep Boys.

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    Also remember that at 90K miles, you

    could very likely profit from a new MAF sensor. If you have to go to the trouble of removing it, why not put in a new one? It's a critical part in the proper and economical operation of your motor.
    Clean it and you might still not solve your problem even if it's the cause. They do wear out.

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    Thanks, KeithS and Stinger9. I may consider

    replacing it if it's quite a hassle to remove the housing. I'll take a look and may get the BMW tech to do it. Yes, I heard the sensor must be dry before re-energizing.


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    tom busby
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    Re: Fault codes P0171 and P0174

    I have these faults too, and I cannot find the problem, on a 325i with 101,000 miles. The light comes on at de-accellerating in 5th gear from 75mph to 65mph. I can clear the codes, and sometimes the light goes off by itself. The car runs fine, and all OEM maintenance is up to date, including new O2 sensors. I have cleaned the mass air flow sensor with CRC, and replaced the throttle body-to-manifold gasket, and replaced the vacuuum line to the gas filter, and none of the rubber intake tubes/boots are leaking. I think I will have to buy a new mass air flow sensor.

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    How do they wear out?

    How do they wear out? There are no moving parts. I realize they can go bad, but don't think it is really the same as wearing out. Regardless the CRC costs about $6 and it took me less than 10 minutes start to finish. Think it's worth trying to clean it first.

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    Good question. I don't know what causes them to

    to fail, but I found reference to their fragility.



    Q: What does the code P0102 mean?

    A: The code P0102 reads "Mass air flow circuit low input". There is a certain procedure to test Mas Air Flow sensor (MAF) for proper operation. When you bring your car to a dealer, they will perform this procedure to check if the sensor is faulty. Mass Air Flow sensor failure is very common.


    The Air Flow Sensor or Mass Airflow Sensor (MAF) is one of the components of an electronic fuel injection system and is found in many of modern vehicles. The Mass Air Flow sensor is usually installed inside the intake air duct between the air filter and the engine. The Mass Air Flow sensor is used to measure the amount of air entering the engine. This measurement is used by the engine computer or ECM to calculate proper amount of fuel injected into the cylinders in order to provide optimum combustion and low emissions.
    Problems with Mass Air Flow sensors are common. Bad or contaminated Mass Air Flow sensor can possibly cause a wide range of various vehicle driveability problems such as stalling, especially when the engine is cold, misfiring, poor acceleration, etc.
    In addition, a problem with the Mass Air Flow sensor often causes the "check engine" or "service engine soon" light in the vehicle instrument panel to illuminate.
    The "check engine" or "service engine soon" light comes on when the engine computer detects some fault in one of the components of the emission control system.


    But Keith, I do agree with you that replacement is worth a try if you don't mind the possible extra change-out.

  12. #12
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    I checked the MAF sensor and cleaned it with Q-tip

    but the sensor looked pretty clean. I got hardly any dirt on the MAF. After I remove the MAF, is it safe to spray that CRC cleaner into the air intake without taking anything else apart? Is there another sensor inside, before the throttle body? I saw Tom Busby's post on e46fanatics.com

    http://forum.e46fanatics.com/showthread.php?t=397536&highlight=p0171+code

    Claims that throttle body gasket was bad and had to be replaced, causing minor leak. I tend to think I have a small vacuum leak before the throttle body because it is triggering both bank 1 and 2 errors. I sprayed WD40 to check vacuum leak but I could not find it. BMW tech said he usually finds a tear at the "Y" or near the bottom but he didn't find an obvious tear in mine. I think I will wait a little but I may replace all the rubber boot near the throttle body and the gasket. In any case, I don't think it's a serious issue although I want to take care of it. Car is running better than ever and it's been a great car to me.

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    Tom, I read your old post on e46fanatics.com. I

    don't think it's the mass air flow meter (sensor), otherwise it would trigger a fault code for MAF. I am thinking we both have a very minor vacuum leak before the throttle body because it is triggering bank 1 and 2 errors. I would suggest replacing all the rubber boots first, even though they look fine. I always get my parts at taylorautomotive.com. I think the air flow meter (sensor) with the box is $300 but it's $500 at dealer. Anyway, I won't replace the MAF unless the error code triggers. May be I can get the BMW tech to check the MAF resistance/voltage or something. Anyway, can you please email me at [email protected] to keep me posted when you take the next action step. I will do likewise when I get your email. Thanks!

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    You may want to clean your fuel injectors....

    I did it at the lube shop yesterday and car runs a lot better cause injectors were dirty even though I use FI cleaner in gas tank all the time. I also cleaned the throttle body. Also, I found out that P0171 and P0174 codes could be attributed to a number of things including vacuum leaks (usually torn rubber boot), dirty fuel injectors, or bad MAF. So you will have to do the process of elimination. Bad MAF also has its own error code..so I doubt it's the MAF. Anyway, I reset the SES light and will see what happens. Since I have no vacuum leaks, my problem could be the dirty injectors.

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    I am in the process of diagnosing this

    but it's happening on my wife's Ford Explorer not my 323i. It's due to a leak in the intake system and there are many possible places it can happen. Here's the case of the Explorer....

    On cold mornings, the Explorer idles rough to the point of dying and goes back to normal after it warms up. The codes are triggered because of the system detected a lean fuel mixture. While it's idling roughly, I sprayed WD40 all around the intake manifold and I think there's a leak in the intake manifold gasket. I did some more search on the internet and found a "campaign" dealing with this exact issue, not a recall, by Ford some time ago which, of course, has already expired. Turns out the intake manifold gasket in my wife's Explorer is crap. It shrinks in cold temps to the point of creating a leak that closes up when it warms up and expands. Labour, according to the stealer, will be close to CAD$1000 range so I just ordered the kit (CAD$80) and I'll try to do it myself.

    Edit: Forgot to add that in Ford's "campaign", the cam chain tensioner rattling issue is included and a replacement part is included in the $80 kit. I do hear this rattling once in a while and hopefully will get addressed as well.

    Edit #2: I also tried cleaning the MAF and ICV a couple of times without success. I took it in to an independent shop and was told the O2 sensors may need to be replaced and a full tune up as well. I didn't accept this recommendation because when I clear the codes, they only come back when the temps go down to about 5 degrees Celcius. All is well when the temps are higher than that.

    Jos

  16. #16
    Jos
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    Update: New intake manifold gaskets installed

    Leak sealed and problem fixed. Cold idle is back to normal and codes P0171 and P0174 did not come back.

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    Finally fixed problem with P0171 and P0174...more

    Well, I got the above error codes 6 months ago and tried so many different things but didn't fix the probem. I had cleaned the MAF, fuel injectors, changed plugs, air intake rubber boots (it was not leaking like most folks think), and air filter and the problem still persisted after 500-600 miles. BMW shop could not figure out the problem....told me it could be a vacuum leak but could not find any leaks. Finally I removed the air adjuster unit as shown in link http://forum.e46fanatics.com/showthread.php?t=342081. My unit was not broken, just dirty.

    Apparently, the adjusted unit was dirty with oil sludge and it kept the plastic "flap" from moving freely (the web link above will give more details). I cleaned the adjusted unit flap and gasket area with engine degreaser. The car ran like it was brand new...very smooth idle at 700 rpm and accelerates very strongly. Also, after several thousand miles the error codes never came back....usually comes back after 500 miles. So I know I fixed the problem and I wanted to share it here so we have the info on archive. I know some people changed the MAF and fixed the problem but error codes P0171 and P0174 are very tricky to diagnose and could be due to a number of different things. Car is 02 325i with 98K miles.

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