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Discussion Starter #1
My car threw this code today after a little bit of spirited driving on the freeway...

"Check Engine Light P0171 - System Too Lean (Bank 1)"

I only drove the car long enough to get the CEL checked and go home. The car still drives perfectly fine, but I also haven't pushed it since the light went on. The dash light doesn't flash, it's just on.

The only mod I have done is a Simota Aeroform II intake, which I have had for almost 2 years without any problems. When I got home I did a quick check of all the wiring and connections and everything looked fine. The car only has 14,000 miles on it so the spark plugs and all other hardware are practically new. I have done all (two) required services on time.

I tried searching but couldn't find a solid answer...Any ideas what could be wrong? Is this a code that will go away on its own after a few days of driving without issues? If not, I plan to put the stock airbox back in and take it to the dealership.
 

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Lean codes typically mean vacuum leak somewhere. But all kinds of things can fail and give you a leak.

Basically the leak has to be downstream of the MAF, meaning the leaking air is unmetered, otherwise you would not get a code.
 

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WIS diagnostic procedure calls for:
1. Check for correct software
1. Check for exhaust leaks before sonde
2. Check fuel pressure
3. Check fuel pump flow rate
4. Replace MAF
 

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As long as the problem is not directly related to the aftermarket air box (unlikely) then you don't have to take it off for warranty work.
 

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I don't have the 2008 WIS; mine only goes to 2007. But this is a pretty standard DTC. It could mean insufficient fuel as xp3 indicated.

Not sure what "sonde" means. But maybe means exhaust leak before the oxygen sensor.

If you plan to take car to dealer, I would definitely replace stock airbox. Many, if not all, techs are going to look at a lean code and zero in on your intake. From their perspective, 9 out 10 street mods just mess up the car. It will take you less time to put the old intake in than it would to educate/convince the tech.
 

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I don't have the 2008 WIS; mine only goes to 2007.
If you plan to take car to dealer, I would definitely replace stock airbox. Many, if not all, techs are going to look at a lean code and zero in on your intake. From their perspective, 9 out 10 street mods just mess up the car. It will take you less time to put the old intake in than it would to educate/convince the tech.
Definitely.

Remove it, clear the code and drive around for a while to see if it comes back before taking it to the dealer.
 

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Discussion Starter #10
just put the stock airbox back in. its such a ****ing hassle to tighten the flange that connects to the turbo.

i contemplated disconnecting the battery to clear the code to see if i get another cel but i dont want to risk damaging my engine so im just going to take the car to the dealership tomorrow hopefully.
 

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Discussion Starter #11
Wow I feel like an idiot....I took my car to the dealership and a few hours later they called me back and said the problem was a loose gas cap.

That being said, if anyone is interested in purchasing a used Simota Aeroform II intake, send me a PM. I don't want to go through the trouble of reinstalling it.
 

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Someone can do a search, but I don't recall a loose gas cap ever giving a p0171. That doesn't even make sense.

The gas cap code is generated when the ECM performs a leakdown check on the fuel system. Basically the fuel system is pressurized, the final pressure is detected, and then the pressure is checked after 30 seconds or so to see how much (if any) it drops. The purpose is to confirm the integrity of the fuel system so as to prevent loss of hydrocarbons to the atmosphere. In other words it's an evaporative emissions check. This has absolutely nothing to do with how your car actually runs.

p0171 is a lean code. The condition is detected by the oxygen sensor, which is analyzing exhaust fumes. The oxygen sensor reading has everything to do with how your car actually runs.

Sorry, but the tech who told you this has no understanding of modern engine or emissions management.

It is possible he cleared the code and you will not get it again because it was your intake that was actually the problem all along. Maybe you were running right at the border of almost too lean, but only recently you leaned out enough to throw the code. Whether or not you throw the lean code has to do with your long term fuel trim (which is how the ECM compensates for a slight chronically lean condition). Once the lean condition exceeds the capacity of the LT fuel trim to compensate, you get the code. The only way to check things like fuel trim is with a scan tool.
 

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loose gas cap from a tech pov does not make much sense at all! typically that will give an evap emissions code such as a 'small leak'. the bank 1 lean code or even bank 2 lean code most of the times can be traced down to an intake gasket leak, which will allow in enough unmetered air to throw the cel.
 

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A lose gas cap can through all kinds of very strange codes in modern cars...
I googled p0171 and gas cap and could only find more evidence of people trying this solution (i.e. replace gas cap) only to find that it was not the problem.

If I had to bet money knowing what I know in this current case, I would bet it was problems with the Simota intake. You would need to hook up a scan tool to check the fuel trim with the Simota. But if the tubing diameter near the MAF is even a tad larger than stock, it will skew toward lean (yes, the MAF transfer function is that sensitive). Slight chronic lean conditions can be compensated by the long term fuel trim, that's why it exists. Any small leaks downstream of the MAF may push the A/F too far lean. I would suspect a leak right at the attachment point of the MAF. Any irregularities of the gasket could do it. Hose clamps are less likely because they apply pressure over the full circumference of the tube. But the MAF is held against its gasket by only a few screws.

Dirty MAF is possible too.

The thing to do is drive the car and look at the fuel trims with a scan tool now that you have reverted to stock airbox.

Here's a good guide explaining how the tech should approach this code:
http://repairpal.com/OBD-II-Code-P0171-and-P0174
Watch the youtube video as it shows how you can use fuel trims to quickly determine if it's an air leak or not. Good, accurate video! Where are these techs??? Out making videos and not fixing our cars!
 

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I am leaning to believe Simota threw the code.
Gas cap is a very common excuse at every dealership
when they either have no idea what's the problem or
don't want to do anything.
 

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Discussion Starter #17
yeah i find it hard to believe its the gas cap as well. i might be in denial but i really dont think its the intake, only because ive had it since fall 08 without a single issue.

i drove the car about 15 miles from the dealership home on the stock intake and gas cap tightened till it wont click anymore any no CEL. lets hope it stays that way.
 
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