# P0171



## hermes350GT (Oct 18, 2013)

Driving home the CEL came on, hooked up my bluetooth scanner and returned this code. Any Ideas what to look for?


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## l88m22vette (Mar 2, 2006)

Its the precat o2 sensor, and is registering a lean condition. Could be clogged injector, old fuel filter, failing fuel pump...


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## hermes350GT (Oct 18, 2013)

l88m22vette said:


> Its the precat o2 sensor, and is registering a lean condition. Could be clogged injector, old fuel filter, failing fuel pump...



I just changed the fuel filter this past Sunday so that can't be it. I read it could be the PCV system or vacuum hoses.


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## l88m22vette (Mar 2, 2006)

Did you install it in the correct direction? If you just did the filter and just got a CEL which is related to fueling I'd start there, then work on other things once you're sure its not that variable.


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## hermes350GT (Oct 18, 2013)

l88m22vette said:


> Did you install it in the correct direction? If you just did the filter and just got a CEL which is related to fueling I'd start there, then work on other things once you're sure its not that variable.



Yes, the arrow is pointed towards the front of the car


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## lite1979 (Sep 9, 2005)

My money's on a vacuum leak. Check under the intake manifold. You should find two small vacuum lines. I bet one of them is torn right where it meets the intake manifold or very close to it.


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## hermes350GT (Oct 18, 2013)

lite1979 said:


> My money's on a vacuum leak. Check under the intake manifold. You should find two small vacuum lines. I bet one of them is torn right where it meets the intake manifold or very close to it.


on the left or right side? can't really get a good look


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## lite1979 (Sep 9, 2005)

On my stock AMU (225) intake manifold it's on the left, right above the alternator. I poked around there with the engine running, and hearing the hissing noise change when I put my finger on the right hose was how I determined which one it was. You'll probably have to remove that bracket that the dipstick goes through to get to it.


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## hermes350GT (Oct 18, 2013)

lite1979 said:


> On my stock AMU (225) intake manifold it's on the left, right above the alternator. I poked around there with the engine running, and hearing the hissing noise change when I put my finger on the right hose was how I determined which one it was. You'll probably have to remove that bracket that the dipstick goes through to get to it.


Ok, I'll probably get a bunch of different size silicone hoses and replace them all. Also, if I wanna replace the pcv system as well would this kit be sufficient? http://store.034motorsport.com/breather-hose-kit-early-audi-tt-225-amu-reinforced-silicone.html


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## 180dan (Apr 4, 2011)

hermes350GT said:


> Ok, I'll probably get a bunch of different size silicone hoses and replace them all. Also, if I wanna replace the pcv system as well would this kit be sufficient? http://store.034motorsport.com/breather-hose-kit-early-audi-tt-225-amu-reinforced-silicone.html


034 makes the standard for pcv kits. Definitely go with them. Pass on the billet valve option. Get a dipstick tube for 5-$6. You'll brake it during pcv install.


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## lite1979 (Sep 9, 2005)

That kit's pretty pricey, imho. My PCV problem was at the 90 degree elbow, so I just replaced that one part. That shouldn't affect your air/fuel levels, though. Those two small vacuum lines should be long enough to where you can just cut off the damaged part and re-connect the hose. Even if you have the new stuff on the way, it's still better to drive around with no fault codes or boost leaks, and it's basically a free fix.


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## hermes350GT (Oct 18, 2013)

ok so I can't really find/see a vacuum leak however I'm pretty sure I hear one. I still have those braided hoses and I can see slight cracks round where they connect. is this a good hose kit to get? http://www.siliconeintakes.com/liqu....html?osCsid=00e2c315eee8ba155be8122429bce0c9


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## spydox (Apr 4, 2013)

*Vacuum Leak*

There is a Plastic "Y" under the intake manifold that can break into 2 pieces. Its difficult to evaluate- remove the dipstick housing with a bright lite and mirror you can get an idea of whats up under there. I replaced the Y and use Silicone hoses to rebuild the line all the way back to the master cylinder, and my codes went away.


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## hermes350GT (Oct 18, 2013)

So I was cleaning my maf hoping to remedy this problem and I was looking over the hoses and found this. Could that be the problem?


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## lite1979 (Sep 9, 2005)

Yes!


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## hermes350GT (Oct 18, 2013)

Haha ok! What's strange is I'm still hitting 15 lbs of boost. So I wonder.......


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## hermes350GT (Oct 18, 2013)

Ok I've been busy with school so today I had the chance to change that hose coming off the top of the DV (will do all the other lines sometime this weekend). However, my vacuum readings haven't changed and I'm only hitting like 13lbs about boost instead of 15


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## hermes350GT (Oct 18, 2013)

And the CEL came back on after I cleared it too


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## lite1979 (Sep 9, 2005)

Sounds like you still have a leak somewhere. Ideally you should have it smoke tested, but if you listen for the hiss of unmetered air getting sucked in you can usually find it.


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## hermes350GT (Oct 18, 2013)

Ok I heard some hissing coming from the FPR I think


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## lite1979 (Sep 9, 2005)

That's one of the lines that goes under the intake manifold that I mentioned above.


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## hermes350GT (Oct 18, 2013)

lite1979 said:


> That's one of the lines that goes under the intake manifold that I mentioned above.


Ok thanks I'll do that next when I get the chance


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## hermes350GT (Oct 18, 2013)

Turns out my dipstick tube was also cracked as I barely brushed it with my arm and it spun 360


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## hermes350GT (Oct 18, 2013)

Ok for the hose that connects to the bottom of the intake manifold, how do I undo it? and how do I secure the new line? and will 4mm be ok for that?


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## lite1979 (Sep 9, 2005)

It should pull right off, and there will be two of them, one behind the other. A small spring hose clamp should be fine, and 4mm will be fine as long as your clamps are good. It's very likely the OEM spring hose clamp is still on there, and you can re-use it if it's not too loose. The clamps can be bought at any of our local parts vendors, but sometimes you have to get a variety set depending on the store. I have a half-dozen in my basement if you want to grab them.


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## hermes350GT (Oct 18, 2013)

Ok thanks. Oh and I know you said you needed some lengths of hose so I got the shop kit


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