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Check Engine Code P0171 Bank 1 System Too Lean

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Check Engine Code P0171 Bank 1 System Too Lean

  #1  
Old 07-14-2011, 07:41 AM
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Default Check Engine Code P0171 Bank 1 System Too Lean

I recently got a check engine light on my 2001 A4 Quattro with about 130K miles. I ran the code and it was P0171: Bank 1 System Too Lean.

After doing some reading, it appears that it is either an 02 sensor, MAF sensor or vacuum hose leak around the engine. I replaced my MAF sensor not 5 thousand miles ago, so I'm pretty confident it's not that. Personally I think it's a vacuum hose leak, but I'm not sure how to go about checking for that..

Should I just inspect hoses around the engine while the car is running and listen for a hissing noise or something? I know its easy and cheap to replace them so I'm more than willing to do it myself, in fact I don't want to bring it anywhere because every mechanic I've been to screws me or tries real hard to.

If anyone has any other suggestions as to what might cause this code, I am open to advice. I realize a lot of things can cause a code like this to pop up so I'm not ruling anything out just yet, but I'm pretty confident it's a vacuum hose leak.

Thanks
 
  #2  
Old 07-25-2011, 06:04 PM
gimmespeed101's Avatar
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i had the same check engine code.. i first put in the front o2 sensor and that didn't do anything, but after replacing the MAF sensor no more problems and the light hasn't come back on. maybe you got a bad maf sensor the first time.
 
  #3  
Old 07-25-2011, 07:02 PM
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This is more likely an O2 sensor, but checking the other avenues out wouldn't hurt.
 
  #4  
Old 07-25-2011, 07:20 PM
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Location: Northern NJ USA
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I'll assume you have a 1.8t. Check the hoses on the left side of the engine for leaks.
 
  #5  
Old 08-06-2011, 02:19 AM
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Originally Posted by gimmespeed101 View Post
i had the same check engine code.. i first put in the front o2 sensor and that didn't do anything, but after replacing the MAF sensor no more problems and the light hasn't come back on. maybe you got a bad maf sensor the first time.
I have an aftermarket MAFs and an OEM one, which both came with the car. My aftermarket triggers that CEL with that P00171 ODBII code but i get way more boost from it, my engine is also chipped. but i put in my OEM MAFs to pass inspection so check that out if you didnt
 
  #6  
Old 08-06-2011, 09:11 PM
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Location: Encinitas CA
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If you have a 1.8T, check the 3.5mm / 1/8" vacuum line from the intake manifold to the diverter valve, in addition to the more obvious ones. Have a look at the big rubber elbow at the back of the intake manifold -- mine was decomposing from the inside out.

If you cannot find any leaks, the already-suggested O2 sensors and MAF sensor are good bets as well, but obviously costlier to replace.
 
  #7  
Old 02-27-2018, 08:22 AM
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Default 2.0l Tfsi TT

Got the same code on my wife’s TT 2.0l TFSI, only done 53k and was serviced at 50k, checked all hoses and no leaks.
 
  #8  
Old 03-12-2018, 11:35 AM
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Join Date: Aug 2017
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Try,

1. Clean MAP sensor (there is a special two can cleaner set at any auto parts store)
2. Check carefully for leaks loose hoses in on and around the manifold with a good light.

Note: listen for a hiss or a whistle sound when you step on accelerator.

Mine had a bad elbow and a vacuum hose that kept coming off. So I would fix it then it would pop off and happen again.

3. Then evaluate test O2 sensor with VAG or similar tool.
 
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