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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 03-26-2017, 11:38 AM
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halltristan halltristan is offline
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Recurring P0171 and P0174 code

For some time now I have repeatedly had a check engine light and the following codes:

P0171 Bank 1 system too lean
P0174 Bank 2 system too lean

Everytime I erase the codes, they return in about a week. CCV has been replaced. I clean the MAF sensor every year. What else could be the cause?
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Last edited by halltristan; 03-26-2017 at 11:41 AM.
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  #2  
Old 03-26-2017, 01:49 PM
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http://forum.e46fanatics.com/showthread.php?t=897616
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  #3  
Old 03-26-2017, 01:53 PM
pack horse pack horse is offline
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I would check for vacuum leaks first.

Since you have replaced the CCV check the lower intake boot, ICV and DISA for leaks and all the CCV connections.
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  #4  
Old 03-26-2017, 02:26 PM
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When you run out of other ideas, get it smoke tested....it might be something like a cracked valve cover, or leaking VCG....
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  #5  
Old Yesterday, 11:29 AM
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If it's not vacuum leaks (I don't think so), it's the MAF. It soft fails over time.
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  #6  
Old Today, 06:33 AM
marcozandrini marcozandrini is offline
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Quote:
Originally Posted by SeanC View Post
If it's not vacuum leaks (I don't think so), it's the MAF. It soft fails over time.


I've never heard of a bad MAF causing those codes. Smoke test first.


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  #7  
Old Today, 07:09 AM
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SeanC SeanC is offline
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I've never heard of a bad MAF causing those codes. Smoke test first.


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Now you have. Check out my thread over at e46f.c with the title "advanced maf question...."

MAF has been known to underreport overtime causing lean codes for a while. Vacuum leaks causing lean codes usually are accompanied by other symptoms such as rough running, unstable idle, etc.
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  #8  
Old Today, 08:10 AM
Manbearpig77 Manbearpig77 is online now
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I had this issue. I replaced the ccv behind the plenum on my 4.4L. Replaced the maf sensor. Ended up being a vacuum leak on the throttle body gasket. Fixed that, no more codes!

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