# Solving P0171 Code: The Complete Guide



## eaglecat769 (May 4, 2008)

I will update this post as I take pictures, and make additional DIY posts and add links to them here. I have spent too much money solving my P0171 - Bank 1 Lean due to bad or incomplete information here. So, here's my attempt to rectify. While mad at the money I spent, I will feel better if I save YOU money. So please, bump this, and e-mail me a pic of you doing your job. Will make it kinda worth it.








Common Code on Mk IV 1.8T Engine, as given by generic OBDII: 
P0171 - Bank 1 Lean
What does it mean? (Generically)
Too little fuel or too much air during combustion, according to sensor readings of exhaust gases.
What is usually the culprit? (Generically)
80% Chance: Leak in breather system, see two most common causes below. This leak allows extra unmetered air into the intake. Also that big red book I spent all that money on, the Bentley, guess what, it does not cover the breather system 1 bit. Leaves it out. And it is a common failure point. Lovely.
15% Chance: Clogged fuel filter (EASY to do, BUT have patience with connectors. Good DIY's already out there, I'll link to them tomorrow when I update this.)
5% Chance: Leak in larger turbo lines, vacuum side specifically. (Boost leak would release air, making less air and more gas, or a rich condition.)
Two actual most common causes:
1) Y-Hose on top of engine underneath smaller plastic cover.
http://www.ecstuning.com/ES517896/ ($40)
2) S-Hose (sneaky punk) under metal plate holding dip-stick right under intake
http://www.ecstuning.com/ES240211/ ($35)
I obtained sturdier silicone replacement versions for BOTH from INA engineering for $80 shipped 3-day select. Price comparable. Stealership will charge $75 for junk rubber version of Y-Hose alone. I have AWP engine prefix VW Jetta 2003. Be careful when ordering from either INA or ECS to ensure you are obtaining correct item, as there was a dia change mid-year to the S-hose if I recall correctly. Also, S-Hose may be ordered by your local NAPA for $10.79.
Common WRONG information from VWVortex found during search:
1) "Problem is Oxygen Sensors" - The fact that it has read the sensors and interpreted the data from them to produce the lean code means that the sensors themselves are in working order. The sensors have a tendency to fail more often than "slip outta spec". When failed, will be different code, and car may have obvious performance issues.
Common UNLIKELY cause info found on VWVortex during diagnosis:
1) "Problem is MAF" - Mass Airflow Sensor. If your car runs relatively smoothly as did mine, maybe a smidgen less power, however it does not misfire, it, well, runs for lack of better description, just fine... maybe just a tad slow... then it is NOT your maf, and you need NOT spend $150-$300 on new one. Mine was fine, but I didn't know that. I wasted $210. Anyone with misfires that needs a gently used MAF for AWP engine prefix MkIV... contact me, we'll arrange something.
2) "Problem is Noisy Smog Pump" - As it turns out, smog pump (aka SAIC (secondary air injection)) does have a bad design flaw. They used rivets. The bottom rivets nearest road crud (ice, salt, water) tend to rust and the case pops slightly open. Then, at startup, you hear the nasty sound of the venturi affect, but low pitch, as it sucks thru the crack. I wish I'd known (that since mine did NOT have any white lube/corrosion drool) that $5 worth of long mini-bolts and rubber-insert lock washers from the ACE Hardware to replace the rivets (after drilling them out) would have done the trick. Instead of wasting $300 on a new one. Anyone who wants a gently used smog pump, rivets replaced with bolts complementary, contact me. At any rate, that is NOT likely the source of your P0171, just a simple $5 + 1 afternoon annoyance to fix. Well, 1 afternoon granted I help out and post a DIY. Anyone have pics? I don't want to redo.  But on request, I will. Ultimately, this is only a "nice to have fixed" though.
So... that is it for now folks. Updates to come. Just wanted it out here ASAP. I couldn't figure out on my own it was the S-hose and the local stealership lifted $115 out of my wallet to tell me that, AFTER I spent lots of money on phantom fixes I did not need, due to bad information. At least I showed the stealership my "flare" when they wanted an additional $232 to put in a rubber (non silicone) replacement for that S-hose which gets slit due to fowling. Tomorrow morning if not too cold here in IL I will take extensive pics and make a DIY for the S-Hose replacement. I (to make me feel good and know that was it) put in a rubber one while waiting for INA Engineering silicone replacement to come. (only took 3 days, but I'm impatient). If you cannot wait, and have hose in and and have questions, hit me up on AIM (same name). Or, follow opening pics of DIY for thermostat replacement to get access to needed region. Also, if you have the code and cannot wait to diagnose, either carefully when warm, or once engine cools, from driver side, stick your hand under the black plate just under front of intake that holds dip-stick-holder and feel around til you find this S-Hose. I bet you it is split down the middle on the bottom as mine was. Turns out, Audi even did a recall on this hose for the 2002, if my sources are accurate. Shame on you VW. Shame on you.
- John


_Modified by eaglecat769 at 3:12 PM 12-18-2009_


_Modified by eaglecat769 at 3:36 PM 12-18-2009_


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## DrewbyDub (Dec 18, 2009)

*Re: Solving P0171 Code: The Complete Guide (eaglecat769)*

Nice write up my friend...good information as I'm sure we've all experienced this lovely DTC at some point. I actually replaced my Y-hose last week w/ Eurojet's silicone after finding two huge gashes in the stock POS hose...ended up rippin that "T" hose/breather tube at the connection to the y hose in the process...went w/ the electrical tape route for time being










_Modified by DrewbyDub at 9:50 PM 12-21-2009_


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## blueapplepaste (Aug 17, 2002)

Just to add my experience, I had the same code but mine ended up being a cracked a brake vaccum pipe: http://www.ecstuning.com/Search/Brake_Vacuum_Hose/ES308112/

Replaced it and code was gone.


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## liquidvw (Mar 20, 2003)

Thanks for the write up. I just got the P0171 on Monday. My issue sounds just like yours. The car runs fine, just a little less power. I haven't had the time to find the hose that is causing my issue, but when I do I'll post what I find.


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## kroutbrner (Nov 2, 2009)

I have this code often as well. I also recently discovered the ripped hose at the "t". It will be replaced soon.

Thanks for such a great write up.
Cheers:beer:
-Ross


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## Oh_My_VR6 (Sep 6, 2004)

I just want to know what your "Flare" is? :sly: :laugh: :thumbup:


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## liquidvw (Mar 20, 2003)

I figured I would update this post just in case someone searches in the future. I found the issue. The hose that goes from the PCV valve to the bottom of the intake was torn. Hopefully that's the only broken hose. I ordered it from 034. Only $13. 

06A 103 221BK

http://www.034motorsport.com/engine...mk4-18t-block-to-intake-manifold-p-19101.html


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## Kawcrash (Mar 22, 2008)

*P0171*

I got an email from my wife this morning. My 2004 GTI 1.8T with 111,000 miles acted like it ran out of gas, it has 1/2 tank, and flashed P0171. Did your car continue to run with the torn S and Y hoses? Could it be a failed fuel pump


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## liquidvw (Mar 20, 2003)

Kawcrash said:


> I got an email from my wife this morning. My 2004 GTI 1.8T with 111,000 miles acted like it ran out of gas, it has 1/2 tank, and flashed P0171. Did your car continue to run with the torn S and Y hoses? Could it be a failed fuel pump


My car ran OK with the cracked hoses. I drove it for a few weeks with the hose cracked as I couldn't find the problem at first.


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## Kawcrash (Mar 22, 2008)

Thanks for the information. I will keep looking and post my findings.


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## Trialnterror (May 3, 2013)

What was your problem ? U fix it (2011)


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## Trialnterror (May 3, 2013)

Kawcrash said:


> Thanks for the information. I will keep looking and post my findings.


What was the issue? You've had a couple years!:screwy:


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## DC Jetta Guy (Jul 31, 2004)

blueapplepaste said:


> Just to add my experience, I had the same code but mine ended up being a cracked a brake vaccum pipe: http://www.ecstuning.com/Search/Brake_Vacuum_Hose/ES308112/
> 
> Replaced it and code was gone.


Same thing here.


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## VdubJ3tta (Mar 31, 2013)

Thank you good sir for this write up. Actually no, you are no sir, you are a God. My CEL should get lost after this read.


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## jettalovver (Apr 9, 2014)

*Guide for the "unlikely" Secondary Air Pump Fix*

The OP said he was looking for a DIY. 

I'm currently working on solving this issue. Had misfires before cylinder 1 and 3 and rough idle feeling like it would stall out. Fixed all the hoses and all cracked ones and replaced some for good measure. Solved that but now I have the dreaded P0171.

I can hear the pump doing it's thing on a cold start (venturi effect) sort of sound and was looking for a DIY.

Thought you guys could use this.

http://uk-mkivs.net/topic/9315-step-by-step-guide-for-repairing-the-secondary-air-pump-with-pictures/

Good luck!


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## Bolshevik36 (Dec 16, 2010)

What exactly is the S-hose called? I have a lose hose and I cant figure out where it goes, any help?


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## ballergti (Nov 17, 2010)

This is the only code I have and for the life of me can't figure it out. Gonna run logs on Monday at the shop can someone chime in and tell me what logs to run? Also what should I post up on here so you guys can help find the problem tired of poor fuel e economy.


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## my-golf (Jan 7, 2015)

I just recently got an 01 Golf, has not even been a week yet and I have this code and P0300. I found this thread and got really excited when I was looking around and noticed a hose under the intake cracked and leaking. I replaced the hose yesterday and when I started it, it started and then the idle then again, got real choppy like its firing on two cylinders or running out of gas. All the other hoses seem to be intact, no smell of oil or anything under the hood. I am not sure what I am going to do, it's -3 out right now so its not like I can just start taking everything apart until I find the problem, that what I would be doing if it was much nicer out.


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## Algeria (May 8, 2013)

When I drive under One quarter tank of gas my fuel randomly shuts off and my car stalls even while moving. As of two days ago, whenever I be driving normally and then when I get it more throttle the fuel just gets cut off and I don't accelerate. This is more pronounced when I am on my tune but still happens in stock mode. With the tune it feels like something is exploding when I go full throttle the car just chokes very aggressively and I hear like a boom coming from the hood. I scanned my car because an engine light came up today finally and I get code P0171. I actually did a 3 step fuel system clean yesterday, and replaced the fuel filter with a new one while I was at it. I got a new air filter and sprayed down my MAF with a MAF cleaner kit and let it dry overnight. I know I didn't out the MAF in the wrong way or anything, and my idle actually sounded a little better than yesterday once I put it back.. So the engine code must be a delayed one from whatever was happening before. I'm in the process of undoing my fuel pump so I can call my local VW parts dealer and let them know to order either the one that threads into the gas tank or the one that has tabs (They said there are two part numbers and they don't know which one mine has. 2005 mk4 gti 1.8t came from USA with stock 17 arrietas and AWP motor). I really hope it's the fuel pump cause I'm running out of ideas otherwise.


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## groggory (Apr 21, 2003)

Algeria said:


> When I drive under One quarter tank of gas my fuel randomly shuts off and my car stalls even while moving. As of two days ago, whenever I be driving normally and then when I get it more throttle the fuel just gets cut off and I don't accelerate. This is more pronounced when I am on my tune but still happens in stock mode. With the tune it feels like something is exploding when I go full throttle the car just chokes very aggressively and I hear like a boom coming from the hood. I scanned my car because an engine light came up today finally and I get code P0171. I actually did a 3 step fuel system clean yesterday, and replaced the fuel filter with a new one while I was at it. I got a new air filter and sprayed down my MAF with a MAF cleaner kit and let it dry overnight. I know I didn't out the MAF in the wrong way or anything, and my idle actually sounded a little better than yesterday once I put it back.. So the engine code must be a delayed one from whatever was happening before. I'm in the process of undoing my fuel pump so I can call my local VW parts dealer and let them know to order either the one that threads into the gas tank or the one that has tabs (They said there are two part numbers and they don't know which one mine has. 2005 mk4 gti 1.8t came from USA with stock 17 arrietas and AWP motor). I really hope it's the fuel pump cause I'm running out of ideas otherwise.


The OEM fuel pump has a very effective surge tank system built into it. My gut instinct for your 1/4 tank or under problem is that the person who installed your last fuel pump did not install the bottom o-ring in the fuel pump basket. These cars will run great right up to the end of the tank...purely because VW is awesome and built us a surge tank for the stock fuel pump.


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## Algeria (May 8, 2013)

groggory said:


> The OEM fuel pump has a very effective surge tank system built into it. My gut instinct for your 1/4 tank or under problem is that the person who installed your last fuel pump did not install the bottom o-ring in the fuel pump basket. These cars will run great right up to the end of the tank...purely because VW is awesome and built us a surge tank for the stock fuel pump.


Ok. Except I don't really care about that problem because I've never had an issue with just making sure I don't go below 1/4 tank. Not being able to accelerate on a full tank and running lean despite having filled up with 94 octane and driving on the stock file is a huge problem however..


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## groggory (Apr 21, 2003)

Algeria said:


> Ok. Except I don't really care about that problem because I've never had an issue with just making sure I don't go below 1/4 tank. Not being able to accelerate on a full tank and running lean despite having filled up with 94 octane and driving on the stock file is a huge problem however..


Your call, no worries.

Have you done an intake pressure test and exhaust leak test, per the faq? Did you find any leaks?


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## Algeria (May 8, 2013)

groggory said:


> Your call, no worries.
> 
> Have you done an intake pressure test and exhaust leak test, per the faq? Did you find any leaks?



Nah, replaced the fuel pump and car is back to normal.


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## groggory (Apr 21, 2003)

Algeria said:


> Nah, replaced the fuel pump and car is back to normal.


Did you put a new fuel pump assembly in or did you just replace the metal fuel pump?


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## nrotteveel (Jan 27, 2015)

Great write up. But was wondering why the issue would not be with the Pressure Regulator valve (i.e. hockey puck or pancake valve)? If there is a lean code, would it not mean that this valve could also fail sending too much air back into air intake? I would think if the lines are clear and not clogged thus if it is not a hose, would it be the hockey puck?


I also have the P0171 code, it came up at highway speed and car just slowed down and then picked back up again. I'm thinking the fuel pump is going and since the sending unit is not giving the correct fuel level, just thought I would replace it. Note I have changed the fuel filter before this error came and I did put in some chevron techron to clean the fuel intake system. 


I don't believe I have any leaks in the S-hose or y hose since they look in great shape. So I don't think I have an issue with these. The other possibility is the PCV valve, but I would like to get your thoughts. I'm new to this car, but it has 100,000 miles on it. It is a 2005 Jetta MKIV 1.8T.


Also, the brakes seem stiff, i.e. takes a fair amount of pressure to stop car as compared to the 2007 Honda Accord I own. So I would assume this might mean that the Suction pump. If the suction pump is failing, I would think this would impact the PCV and thus could also cause the lean issue. 


As a side note, I did run into engine sludge a few months ago which would mean the opposite of the lean code and would mean that I'm not venting.


Would love to hear any feedback on thinking the primary issue is the pressure regulator valve and suction pump. I probably should just replace the suction pump and entire PCV system.


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## nrotteveel (Jan 27, 2015)

Just changed fuel pump. Hope that solves the P0171. we will see. But I broke the stupid plastic clip that holds the electrical connector down. Hate that POS. I thought about drilling a small hole through it to insert a small screw. Just through the black plastic to put pressure on receptor. Bad idea?


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## groggory (Apr 21, 2003)

nrotteveel said:


> Just changed fuel pump. Hope that solves the P0171. we will see. But I broke the stupid plastic clip that holds the electrical connector down. Hate that POS. I thought about drilling a small hole through it to insert a small screw. Just through the black plastic to put pressure on receptor. Bad idea?


Probably a bad idea.

I'd replace that connector with a new one from the dealer and splice into the old wiring. Make sure you know how to do a quality splice with heatshrink and solder. This is a pretty critical piece after all.


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## nrotteveel (Jan 27, 2015)

groggory said:


> Probably a bad idea.
> 
> I'd replace that connector with a new one from the dealer and splice into the old wiring. Make sure you know how to do a quality splice with heatshrink and solder. This is a pretty critical piece after all.


That's funny. I just broke a plastic part like an idiot and you want me to do a quality splice with heatshrink and solder near a gas tank? I will blow my self up.


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## groggory (Apr 21, 2003)

nrotteveel said:


> That's funny. I just broke a plastic part like an idiot and you want me to do a quality splice with heatshrink and solder near a gas tank? I will blow my self up.


That is correct. I want you to cut and splice and solder and heatshrink those wires.

This would optimally be done on the area of the wires that are under the seat. You wouldn't want your splice to be in the tight area of the fuel tank access hole.

Just close the cover before you start working and ensure there is no fuel spilled anywhere. Use your noggin and everything will be good.


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## nrotteveel (Jan 27, 2015)

groggory said:


> That is correct. I want you to cut and splice and solder and heatshrink those wires.
> 
> This would optimally be done on the area of the wires that are under the seat. You wouldn't want your splice to be in the tight area of the fuel tank access hole.
> 
> Just close the cover before you start working and ensure there is no fuel spilled anywhere. Use your noggin and everything will be good.


i have a bad tendency to make the easy look hard.


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## nrotteveel (Jan 27, 2015)

Hello,
After taking a closer look at the PCV breather hose assembly, I noticed that my 90 degree elbow that attaches directly to the valve cover, pn 06A 103 221 BB (or O6A 103 221 AL), that is cracked.


My car is a 2005 VW Jetta 1.8T MKIV GLI and the PCV breather hose assembly doesn't connect with vacuum pump as seen in this image http://www.jimellisvwparts.com/showAssembly.aspx?ukey_product=5185683&ukey_assembly=743893


The question I have is that I'm looking at the 034motorsport breather hose kit 
http://store.034motorsport.com/brea...en-1-8t-awp-reinforced-silicone.html?___SID=U


Note that this looks like it just caps the connection to the valve cover. Just wondering if anyone has done this replacement and whether it will cause other issues by caping that connection? I haven't found anything on the forum for this specific configuration, so I would like your feedback.


I live in California so emissions is a pain in the rear. So don't wont to install if this can cause issues.


Thanks
Nick


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## Cableman (Jun 15, 2008)

*Part numbers?*

Does anyone have any part numbers for the "s-hose" ? The link http://www.ecstuning.com/ES240211 is broken and any reference to "VW MKIV s-hose" isn't super specific about what part this is.

I have been chasing this error code for a while and now I must pass the state vehicle inspection but can't because the CEL keeps coming on with this error. I have replaced the O2 sensor, cleaned the MAF, replaced the water temperature sensor and disconnected the battery to reset the computer each time with no improvement. The only oddity I can see about when the CEL comes on with P0171 is that it happens at idle. If I keep driving, or don't idle too long, I _think _I can avoid the error from showing. I'd like to get a legitimate fix for the problem, however.

Thanks!


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## nrotteveel (Jan 27, 2015)

Cableman said:


> Does anyone have any part numbers for the "s-hose" ? The link http://www.ecstuning.com/ES240211 is broken and any reference to "VW MKIV s-hose" isn't super specific about what part this is.
> 
> I have been chasing this error code for a while and now I must pass the state vehicle inspection but can't because the CEL keeps coming on with this error. I have replaced the O2 sensor, cleaned the MAF, replaced the water temperature sensor and disconnected the battery to reset the computer each time with no improvement. The only oddity I can see about when the CEL comes on with P0171 is that it happens at idle. If I keep driving, or don't idle too long, I _think _I can avoid the error from showing. I'd like to get a legitimate fix for the problem, however.
> 
> Thanks!


I have been going to this site to get specific part numbers. http://www.jimellisvwparts.com/showAssembly.aspx?ukey_product=5185683&ukey_assembly=743893

Not sure what year or engine you have, but the link above is a 2005 MKIV gli 1.8t AWP engine.

But it makes since this occurs at idle. That is when you have the most vacuum. If you use your code reader and if the STFT at idle is above 10 and then if you rev to 2000 RPMs and the STFT goes significantly lower, then it is surely a vacuum leak. If the STFT stays the same, you most likely have a fuel delivery issue.

See this site for more info http://www.aa1car.com/library/what_is_fuel_trim.htm


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## BassNotes (Mar 16, 2005)

Cableman said:


> Does anyone have any part numbers for the "s-hose" ? The link http://www.ecstuning.com/ES240211 is broken and any reference to "VW MKIV s-hose" isn't super specific about what part this is.
> 
> I have been chasing this error code for a while and now I must pass the state vehicle inspection but can't because the CEL keeps coming on with this error. I have replaced the O2 sensor, cleaned the MAF, replaced the water temperature sensor and disconnected the battery to reset the computer each time with no improvement. The only oddity I can see about when the CEL comes on with P0171 is that it happens at idle. If I keep driving, or don't idle too long, I _think _I can avoid the error from showing. I'd like to get a legitimate fix for the problem, however.
> 
> Thanks!


My code kept popping up at idle as well, about once or twice a week. I'd searched all over for some sort of leak. Finally there was only one thing I hadn't really checked: I undid the insulated jacket around the hose on the turbo outlet. I checked the hose and the clamps, and although they seemed OK, I loosened the clamps, pulled the hose and re-seated it, and tightened the clamps back up. That was about three months ago, and the P0171 code has not come back up again.


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## nrotteveel (Jan 27, 2015)

BassNotes said:


> My code kept popping up at idle as well, about once or twice a week. I'd searched all over for some sort of leak. Finally there was only one thing I hadn't really checked: I undid the insulated jacket around the hose on the turbo outlet. I checked the hose and the clamps, and although they seemed OK, I loosened the clamps, pulled the hose and re-seated it, and tightened the clamps back up. That was about three months ago, and the P0171 code has not come back up again.


I don't see how this would solve the issue. It is a Lean code which means there is to much air. If there was a turbo boost leak, you would get less air. Unless you now have a leak in your turbo boost hoses. 

The code will only present if the Long term full trim (LTFT) is above 20-25. I bet you still have a high LTFT, but just not high enough to get the code.


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## BassNotes (Mar 16, 2005)

nrotteveel said:


> I don't see how this would solve the issue. It is a Lean code which means there is to much air. If there was a turbo boost leak, you would get less air. Unless you now have a leak in your turbo boost hoses.
> 
> The code will only present if the Long term full trim (LTFT) is above 20-25. I bet you still have a high LTFT, but just not high enough to get the code.


Here's how it works. A lean code means air is leaking into the intake system. When the turbo is not boosting--that is, _most of the time,_ including at idle, when the code was appearing (the turbo does not start boosting until the manifold vacuum reaches zero anyway)--a leak in the post-turbo intake plumbing will draw unmetered air in, causing a lean situation. I'm glad I don't have that issue any more.


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## nrotteveel (Jan 27, 2015)

BassNotes said:


> Here's how it works. A lean code means air is leaking into the intake system. When the turbo is not boosting--that is, _most of the time,_ including at idle, when the code was appearing (the turbo does not start boosting until the manifold vacuum reaches zero anyway)--a leak in the post-turbo intake plumbing will draw unmetered air in, causing a lean situation. I'm glad I don't have that issue any more.


I see what your saying. But if this was the case, you would have huge swings in the STFT while driving since the turbo only will kick on then. So you will see positive STFT at idle and a huge swing to negative under acceleration. From all that I have seen in the forums, it sounds like this case is more of a vacuum leak then a post turbo leak.


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## Little devil (Jun 15, 2015)

*2005 vw passat turbo 1.8 L p0171, p0300, p0301, p0302, p0303, p0304*

I have a 2005 vw passat turbo 1.8 L 
This car has full engine power, but idles very rough, codes are p0171, p0300, p0301, p0302, p0303, p0304. if I reset the computer it will run perfect until the engine light comes on, (will last up to a week). No vacuum leaks found. EGR is working, and MAF Sensor was replaced. Any help out there?


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## nrotteveel (Jan 27, 2015)

Little devil said:


> I have a 2005 vw passat turbo 1.8 L
> This car has full engine power, but idles very rough, codes are p0171, p0300, p0301, p0302, p0303, p0304. if I reset the computer it will run perfect until the engine light comes on, (will last up to a week). No vacuum leaks found. EGR is working, and MAF Sensor was replaced. Any help out there?


look here http://forums.vwvortex.com/showthread.php?5411153-Help-codes-p0171-p0300


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## Polini33 (Feb 5, 2014)

i too suffer from this code (only recently in the last 2 months) but my car runs, idles, drives perfectly. I have owned the car for 2 years and there has always been an oily smell from the engine when it runs, but no leaks. 

I finally got sick of the oil smell and decided to find which vac lines are broken.

I spent a bunch of time moving wires/hoses and sticking my big hands under the intake manifold to remove the large plastic breather pipe from the top of the crankcase, to find it has a massive hole in it. I tried to remove it, and the bottom of the breather pipe broke and got stuck on top of the cylinder head. I spent hours extracting it, and I finally removed the entire intake manifold and got it out. I then shined a lamp into the oil filter housing thing, and noticed that pieces of the breather pipe have been in there for a long time, and they were clogging up the whole area. i extracted them as best as i could, as they were brittle.

Do yourself a favour and replace this before you get my problem. I am lucky that the car is running well. 

Just ordered a bunch of hoses and the pipe and o-ring from ecstuning, as well as a vacuum suction pump, which was covered in oil and i assume clogged. Will report back if it fixes my code. I am confident it will


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## BassNotes (Mar 16, 2005)

nrotteveel said:


> I see what your saying. But if this was the case, you would have huge swings in the STFT while driving since the turbo only will kick on then. So you will see positive STFT at idle and a huge swing to negative under acceleration. From all that I have seen in the forums, it sounds like this case is more of a vacuum leak then a post turbo leak.


The LTFT has been in the -10 to -13% range. STFT has tended to be in the 0 to 1% range.

The P0771 code had been absent for about five months, then came back twice in the past three days. I don't know why it went away for that long; ironically, it first reappeared just as I was taking the car for its smog check.

After refueling on Tuesday, the car was hard to start. About 50 to 60 miles later that day, I got a P0441 code, which I'd never had before. Wednesday evening I had time to pull out the purge valve (those tamper-resistant hose clamps are a pain in the ass) and test it with a Mity-Vac hand pump and some clip leads. With 12V applied, it's wide open; with no voltage, it's leaky--not open but not capable of holding a vacuum either. I'm awaiting a replacement valve in a day or two. Or three. I'm hoping that cures the evap and unmetered air situations.


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## nrotteveel (Jan 27, 2015)

BassNotes said:


> The LTFT has been in the -10 to -13% range. STFT has tended to be in the 0 to 1% range.
> 
> The P0771 code had been absent for about five months, then came back twice in the past three days. I don't know why it went away for that long; ironically, it first reappeared just as I was taking the car for its smog check.
> 
> After refueling on Tuesday, the car was hard to start. About 50 to 60 miles later that day, I got a P0441 code, which I'd never had before. Wednesday evening I had time to pull out the purge valve (those tamper-resistant hose clamps are a pain in the ass) and test it with a Mity-Vac hand pump and some clip leads. With 12V applied, it's wide open; with no voltage, it's leaky--not open but not capable of holding a vacuum either. I'm awaiting a replacement valve in a day or two. Or three. I'm hoping that cures the evap and unmetered air situations.


I assume you meant a P0171 code. But with a -10 to -13 LTFT, that would imply you are rich, not lean and a P0171 is a lean code. I would have thought you would have a P0172 rich code, but that won't trigger unless it is at -20-25. So I would be curious as to whether the LTFT goes back to near zero after you change the purge valve.


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## BassNotes (Mar 16, 2005)

nrotteveel said:


> I assume you meant a P0171 code. But with a -10 to -13 LTFT, that would imply you are rich, not lean and a P0171 is a lean code. I would have thought you would have a P0172 rich code, but that won't trigger unless it is at -20-25. So I would be curious as to whether the LTFT goes back to near zero after you change the purge valve.


No, I got a P0441 code Tuesday evening, which is incorrect purge flow. First time I ever saw that one, but I should've expected it after the car was so hard to start after the fillup.

I'll connect VCDS tomorrow and see where the trims are in block 032.

It's been baffling to get the P0771 code repeatedly when the LTFT has tended to be in the minus double digits. That's why I was so relieved when it disappeared for a while.


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## nrotteveel (Jan 27, 2015)

BassNotes said:


> No, I got a P0441 code Tuesday evening, which is incorrect purge flow. First time I ever saw that one, but I should've expected it after the car was so hard to start after the fillup.
> 
> I'll connect VCDS tomorrow and see where the trims are in block 032.
> 
> It's been baffling to get the P0771 code repeatedly when the LTFT has tended to be in the minus double digits. That's why I was so relieved when it disappeared for a while.


I think you are right about the P0441 code, but are you also seeing a P0771 or a P0171? That is why I asked if you mean P0171. If you are truly getting a P0771 code, that is a transmission solenoid issue.


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## BassNotes (Mar 16, 2005)

Sorry. Finger dyslexia. It is P0171.


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## RTownVDubster (Jan 28, 2012)

just adding to this seeing as i have just now run into this problem; I have the APR stage 2 tune on my car and I am also running a catless 3" system with a defowler. My car would act like it was going to stall out and would jerk terribly whenever i would smash the pedal to try to get some kind of boost. I noticed that it wouldn't go over 11 psi but normally runs around 18. Unplugged the rear O2 because it was reading steady at .45v (not really changing much) and drove it, now I have full boost, just a terrible idle because the O2 is unplugged. So just a heads up to any one else out here that might be running the same kind of setup.


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## JRoque (Oct 4, 2010)

Hi all,

First, sorry to revive the very old thread. Advise from a newbie: carefully read the first post on this thread and follow the link aa1car. Before you replace your fuel pump, filter, pressure regulator, spark plugs, distributor, etc, etc chasing a P0701 code, go very carefully through all the hoses looking for leaks.

My issue drove me nuts for months. I ended up with P0701 (lean mixture) and P0304 (misfire on cyl 4) codes. The car had little power and it would hesitate and buck under slight power demands and at nearly all speeds. It started fine and as long as the initial mixture has being 'doped' rich during start up, the car idled fine. As soon as that was over, idling was terrible and the occasional valve knock can be heard in the cabin even.

In the end, as with the OP, it was a leaky hose in the MAF/intake assembly. Cutting 1" off and reattaching the same hose was all it took - in the end. I just ordered 12' of silicone hose from Amazon and will be replacing all of those toasted suckers.

BTW, and separate from the main fuel topic here, I also had an ABS warning light on. While chasing the above, I noticed the brake booster vacuum lines 'appeared' attached and fine but were nothing but. Those hard hoses had cracked on the underside where they connect and were leaking. For now, I grabbed my trusty roll of high-temp duct tape and secured every end going to/from brakes. ABS light immediately went out.

JR


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## ludhovik (Sep 18, 2017)

Hello everyone,

Sorry for reviving this old post. 

Can a P0171 code come from a leak or bad catalytic converter? My mechanic quotes me $1200 to change the catalytic converter and the two O2 sensor.

Thanks


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## Bigshooter2 (Jul 31, 2019)

I hope this helps someone of there. Here is my experience;

2003 Jetta GLS, 1.8t, codes, P0171 (SYSTEM TOO LEAN BANK 1), P0304 (CYLINDER 4 MISFIRE DETECTED), P0303 (CYLINDER 3 MISFIRE DETECTED), P0300 (RANDOM MISFIRE DETECTED), P2637 (TORQUE MANAGEMENT FEEDBACK SIGNAL A). 

The car was running rough, lack of power. If I drove it hard there was a dashlight that would blink (triangle shape?? cant remember exactly) and the car would shift hard. I found a couple of hoses that were broken, crankcase breather and another one that tees off from the breather. I replaced the 2 hoses along with the PCV valve. Cleared the codes and then drove the car. No change in the performance and all the codes came back. I then started looking at the MAF sensor. I read somewhere that if the car is running and you unplug the MAF electrical connector the car should start to run rough and/or stop completely. So I unplugged the MAF with the car running and there was no change to the engine while idling but a new P codes showed up; P0413 (secondary air injection switching valve A circuit Open). I decided to clean the MAF and try again. No change to the engine while idling and the car actually seemed to drive worse, lack of power and hesitation when accelerating. I finally replaced the MAF ($150.00) and cleared the codes. Took it for a drive and noticed right away that the car was driving better. I blew clouds of white smoke for the first minute but then it cleared up. I can drive it hard now and it shifts smooth and the codes have not come back.


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## Bigshooter2 (Jul 31, 2019)

I forgot to add that after I replaced the MAF, I did the same procedure of unplugging the MAF while the car was idling and there was no change. Only when I drove the car did I notice the improvement.


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## buckaroo789 (Jul 30, 2008)

*Shame on you VW. Shame on you*

That should have been the very first statement with these VW vehicles - especially the 1.8T's. 

Thanks for posting. 
I encountered this very same problem a couple of years ago. Removing the plastic engine cover revealed all of the Y , S and the PCV valve that feeds into the engine tubes crumbling apart. Here's the link for the complete set from 034motorsport https://store.034motorsport.com/breather-hose-kit-mk4-1-8t-aww-awp-awv-reinforced-silicone.html

These vehicles continue to be money pits unless there are just a few of us unlucky folks who have had bad experienced with this "GERMAN" engineering piece of crap.


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## buckaroo789 (Jul 30, 2008)

nrotteveel said:


> Hello,
> After taking a closer look at the PCV breather hose assembly, I noticed that my 90 degree elbow that attaches directly to the valve cover, pn 06A 103 221 BB (or O6A 103 221 AL), that is cracked.
> 
> 
> ...



Nick,
Its best you call 034. They are based in Fremont, CA. You can send them pics of your issue and they will help you with the right part and address any questions you have.


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## Vap8102 (Dec 24, 2019)

Just wanted to add one more cause for the P0171. 

Like many of you I found a lot of good advice on this forum so wanted to share my experience in case it can help the next poor bastard who struggles through finding root cause. I have an 04 GLI 1.8t AWP with 140k miles. I’m the 2nd owner after the original owner drove it till the timing belt broke and bent all the valves. I got all that fixed and the car ran great, but before long I started getting the 0171 code.

I did all of the things suggested here and still had no luck clearing the code. Replaced the fuel filter, fuel pump, S hose, Y hose, hockey puck, brake booster hose (which was cracked but replacing didn’t fix it), the PCV, the o-ring on the elbow hose at the crank case. Built my own smoker using a 1 gal paint can and some invents and did the smoke test. No leaks.

And then when that didn’t work I got more desperate. Sealed the dipstick around the crankcase, Replaced the secondary air hoses, and replaced that mess of little hoses underneath the intake. I also replaced the forward O2 sensor. 

Around this time, i also started getting a pending code p0507 (in addition to the p0171) for the catalytic converter. 

So I figured I needed to replace the cat anyway. Took it down to a muffler shop and got the cat replaced with an aftermarket (not OEM) cat. I asked the guy if he could see anything wrong with the old one. He said the one he took off was a “high performance” mini cat and sometimes they don’t last long on these cars.

Well I had run out of all hope at this point and I didn’t expect any miracles, but I’m about 700 miles on it since then and no CEL! No pending codes. No P0171!

So at least for me, a new cat solved my P0171 problem.


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## Colookinght (Apr 8, 2020)

Thanks for the information.


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## Tim-NJ (Aug 8, 2020)

*P0171 check engine light on but idles and drives fine*

Having this same P0171 error code on a 2008 Eos 2.0T 74K miles that I just bought. Of course, the check engine light came on first time on the way home from purchasing. Grrrrr! Have read through this very excellent thread and see how it can be endless. In the week since owning, I have cleared the code, driven the car around town for about 90 miles, and had the light come on and off twice without me clearing the codes, which I thought was odd. Its back on presently after about 25 miles. No discernible difference in idling or engine performance to m, seems fine except for the check engine light, its the only code. Have an appointment to have it checked tomorrow but was wondering if the mileage distance driven and the off/on are clues to what may be the cause. To be sure, my basic OBDII reader says its "system too lean, bank 1". And also, it has not been highway driven or up over 60 mph during this week, just around town and idling. TIA.


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