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P0171 Fuel Trim,Bank1 System too Lean

The guys at autozone thinks its an O2 sensor.

Car is a 1.8t with 35k miles.

Please Help :( :( :(
 

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check the vacuum hose going to the DV from the intake manifold. The hose looks like it is covered with a black braided cloth and are prone to dry rot. A crack/split in that hose is the most common cause of a lean running condition.
 

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pacent said:
If a vacuum hose is broken, doesnt that mean air is escaping somewhere and causing the engine to run too rich? :???:
I think it means air is escaping from the atmosphere and into your engine. ;)

Sorry, but really if it was an O2 sensor issue then this would shouw up on your VacCom readout. As mentioned, check all your vacuum hoses.
 

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probably the vac hose - the signal from the o2 sens is lean because unaccounted for air is getting in after the "air measuring" device (MAF) and therefore no fuel is added for the "extra" air. - very common CEL - CHECK THE HOSE FIRST.
 

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At idle & low RPM the vacuum holds the DV open to allow the boost to recirculate and as RPM increases the vacuum drops closing the DV. If the vacuum hose going from the intake manifold is cracked then the DV is closed and the engine has full boost at idle & is running too lean.
 

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What does DV stand for?
Divertor Valve.

I have had that particular code and it can mean anything within the emissions. Try taking apart your airbox and cleaning the MAF (Mass AirFlow Sensor), again as mentioned "check all your hoses" for any cracks or hoses that have become disconnected. Have you done anything within that area of your engine compartment???? Good luck.
 

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No, I have not done anything significant. I got gas the day before and tried the gas cap trick which turned off the CEL for 4-5 days but then it came on and stayed on, so that may have been coincidence.

THe car does seem to surge a bit under acceleration so I'd suspect the MAF or a vacuum hose more than the O2 sensor. I figured I'd check online before popping ~ $150 for an O2 sensor that might not help at all

Thanks,

Tim
 

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OK, we have people talking about two different things... the diverter valve(DV) does not control boost, that's the N75 or waste gate regulator (there's other names also).

The original advice to check the DV vacuum hose is good. While your at it check all the vacuum hoses, but the one to the DV is most susspect.

For the record, the DV allow recirulation of pressurized intake air to be released back into the intake (low pressure protion). This allows the turbo to spin more freely when there is no load (because it's not trying to move immoveable air). The only waty it effects boost is when it fails, and leaks. The DV can never cause there to be too much boost.
 

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I had the same code recently. Cleaning the MAF fixed the problem. Just make sure you use a NON-RESEDUE electric parts cleaner ... and do not attempt to touch the wire sensor with anything.
 

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Hmm,

Got under the hood today and hunted around. Those vacuum lines are pretty well hidden on my engine (AUG)... Nothing seemed loose or bad. The line that goes
from the DV goes under the air intake and is pretty hard to reach.

I thought I saw the MAF on the airbox. I'll check my Bentley manual and make sure I'm looking at the right area. Maybe I'll try that instead of replacing the lines.

Tim
 

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I found my DV hose to have a HUGE hole in one part of it. The hose looked fine every other place, but down in the dpths of the engine it was rubbing and totally destroyed. just replace all vacuum lines. There are usually 2-4 of them. My AEB had 2 and it took me about 1 hr to do. all you need is a flat head for the belly pan, a vice grip to mangle the one time use clamps and new vacuum line. 10 ft will be more than sufficient. 5 is good for an AEB.
 

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It makes sense that there is a vacuum problem as the CEL doesn't come on until I drive the car and get the rpms over 2K or so then decelerate. The CEL comes on as soon as the car decelerates. From what I've read of the DV that would be the point at which the DV would engage to keep turbo rpms up

Tim
 

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Well I have more information about this P0171 CEL. I started trying to replace the vacuum line on the DV and in the process of trying to cut the one-time use clamp off the vacuum connector of the DV I snapped off the tube.

So Monday I ordered a Forge DV. Figured the metal one might be a bit stronger and also ordered 4mm silicone vacuum line. In the meantime the vacuum line is hanging uncconected from the DV.

I noticed this morning that the CEL no longer is on!!! I guess this confirms that the DV/vacuum line was the culprit.

I figured I'd pass along this info in case anyone else has a P0171 CEL and wants to see if it is the DV or its vacuum line

Tim
 

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That vacuum line was the first thing to go on my '98. The hose that they use from the factory is total crap and doesn't last more than a couple years on a new car. Mine had a hole in it where the hose connects to the fitting on the intake manifold.
 

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The DV line on my engine ( AUG ) is very hard to get at where it attaches to the manifold. Maybe I just need a different screwdriver to wedge it open. I see someone used vicegrips. I'm afraid of breaking off the nipple on the manifold
where it attaches.

Tim
 

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DoNotPassatGo said:
Well I have more information about this P0171 CEL. I started trying to replace the vacuum line on the DV and in the process of trying to cut the one-time use clamp off the vacuum connector of the DV I snapped off the tube.

So Monday I ordered a Forge DV. Figured the metal one might be a bit stronger and also ordered 4mm silicone vacuum line. In the meantime the vacuum line is hanging uncconected from the DV.

I noticed this morning that the CEL no longer is on!!! I guess this confirms that the DV/vacuum line was the culprit.

I figured I'd pass along this info in case anyone else has a P0171 CEL and wants to see if it is the DV or its vacuum line

Tim

so you just let the line that goes from the intake manifold to the DV hang?

wouldnt this cause a vacuum leak?

im just tryin to figure out if this could be my problem, or if i can use this method to narrow down my p0171 code.

thanks in advance
 

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DoNotPassatGo said:
The DV line on my engine ( AUG ) is very hard to get at where it attaches to the manifold. Maybe I just need a different screwdriver to wedge it open. I see someone used vicegrips. I'm afraid of breaking off the nipple on the manifold
where it attaches.

Tim
I suggest you replace all your vacum hoses with silicone hoses to prevent any more boost leaks. Plust those OEM hoses are not the best. Make sure u don't break off those nipples. I heard that they're not cheap. I was able to pull some of those hoses off just by pulling on the hose and using a straight screw driver to assist. I woulnd't recomment using vicegrips to pull the one time clamps off. Here is a pic of all 4 hoses that should be replaced. Originally posted by Dan.

 
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