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P0171 Code: Trouble diagnosing

 

Hi everyone,

My 2003 Eurovan has an intermittent p0171 that I can't seem to find the source of the vacuum leak. I first got the code about 5 or 6 years ago, and when I went hunting for a vacuum leak, the brake booster was cracked.? I taped it at first, then replaced it and things seemed better.? Still 2-3 times a year, typically after being on the freeway for a longer period and exiting, the code will come back.? I have tried spraying carb cleaner on all the lines I can find, and don't get any difference.? When I checked the short term fuel trim with an OBD tool it came back at .78% and in reading this thread () it should be something more like 20% when there's a leak.

I'm not really sure what else to do so could really benefit from some troubleshooting advice and things to check.? Any typical leaking spots?? Ways to check other vacuum lines?? At 21 years old, I'm sure there's rubber decaying but damned if I can't find where the heck the trouble is.?

I also have not touched the MAF at this point, assuming that it is happening when I come back down to idle when the throttle body isn't open and air is leaking in.? But maybe that's the wrong conclusion.? Appreciate any advice and troubleshooting steps.??

Thanks!

Menko

--
Menko Johnson

 

On Mon, Jun 3, 2024 at 11:38 AM, Menko J wrote:
Appreciate any advice and troubleshooting steps.
There are a bunch of possibilities shown on the Ross-Tech wiki for that code, so I'd start down the list with testing.

--
Duane
05HD Rialta
227K Miles
 

Thanks Duane,

Any particular trouble spots on the intake to look for leaks or methods to locate them?? I've tried with a stethoscope, but the rest of the engine isn't exactly quiet and can't find it.? Since it doesn't seem to happen all the time, I'm not sure what kind of leak I'm looking for that could be occasional and I don't have much experience trying to troubleshoot these vacuum leaks.

I'll pull out VCDS again and see.? The last time I hooked it up there seemed to be some trouble with the K line I had little or not communications with the ECU, so wasn't so keen to dive that deep into what is going wrong there.?


On Mon, Jun 3, 2024 at 10:39?AM Duane via <txpigeon=[email protected]> wrote:
On Mon, Jun 3, 2024 at 11:38 AM, Menko J wrote:
Appreciate any advice and troubleshooting steps.
There are a bunch of possibilities shown on the Ross-Tech wiki for that code, so I'd start down the list with testing.

--
Duane
05HD Rialta
227K Miles



--
Menko Johnson

 

The vacuum operated PCV valve could be a stealthy leak. The internal diaphragm commonly fails and allows unmetered engine gasses/air into the intake thereby messing with fuel trim. In my case, I noticed residual oil in the intake track, 10-15% lowered gas mileage mostly in freeway travel events,.but no codes. However, my van is a 1999 so not sure if your PCV valve is of similar configuration. It is an easy check. If you can blow into the vacuum port of the valve and it free flows, valve has failed. Good luck!
 

I have heard of a leak happening inside under the dash, the vacuum operates air vent baffles. A mechanic that also owned a 2003 said he fixed his by preventing the passenger side vent from opening. Hope this helps.
 

Thanks for the tip on the PCV, that's a quick check.? Passenger side vent...that's a fun one.? After just having gone in on the blender box door repair let's hope that's not the source =)

I'll keep searching and post back. I'm going to start with the fuel trim monitoring tests to point in the right direction.

MJ


On Tue, Jun 4, 2024 at 12:23?PM Bill Wiggins via <billwiggins=[email protected]> wrote:
I have heard of a leak happening inside under the dash, the vacuum operates air vent baffles. A mechanic that also owned a 2003 said he fixed his by preventing the passenger side vent from opening. Hope this helps.







--
Menko Johnson

 

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I fixed my issue by replacing one of the one way valves , not sure of the part name. The one replaced was new, so it must have been defective.

On Jun 4, 2024, at 3:41?PM, Menko J via groups.io <menkoj@...> wrote:

?
Thanks for the tip on the PCV, that's a quick check.? Passenger side vent...that's a fun one.? After just having gone in on the blender box door repair let's hope that's not the source =)

I'll keep searching and post back. I'm going to start with the fuel trim monitoring tests to point in the right direction.

MJ


On Tue, Jun 4, 2024 at 12:23?PM Bill Wiggins via <billwiggins=[email protected]> wrote:
I have heard of a leak happening inside under the dash, the vacuum operates air vent baffles. A mechanic that also owned a 2003 said he fixed his by preventing the passenger side vent from opening. Hope this helps.







--
Menko Johnson

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