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Old 09-01-2013, 04:48 PM   #551
Scooby Newbie
Member#: 333964
Join Date: Oct 2012
Location: LI NY
2005 sti
aspen white


I have this code and its driving me nuts. I smoked the exhaust and found cracked headers so replaced them with no luck. smoked the intake system and performed a boost leak. no problems. cleabed the mass air flow. no luck. is it a chance that my oxygen sensor went bad due to the exhaust leak and cause this code but no oxygen sensor code?
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Old 09-03-2013, 06:23 PM   #552
Scooby Newbie
Member#: 333964
Join Date: Oct 2012
Location: LI NY
2005 sti
aspen white


Forgot to mention it is running rich as a pig due to it trying to fix the "lean" condition. Wideband shows 10.5-10.8 during cruising speeds. mods are tomei expreme headers and up pipe, ap hard turbo inlet, invidia catless bellmouth dp, invidia g200 catback, cobb ots stage 2 map, doubt it matters but car is sitting on tein springs.
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Old 09-06-2013, 07:42 PM   #553
Scooby Newbie
Member#: 367657
Join Date: Sep 2013
Location: Arizona
2002 WRX


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Old 10-05-2013, 11:52 PM   #554
Scooby Newbie
Member#: 222677
Join Date: Sep 2009
Chapter/Region: SWIC
Location: Scottsdale, AZ
2009 STi


Got this code today and i have no idea why. Idle is normal, boost is normal. I washed my car today at work through our drive thru car wash. Driving home light came on cleared light via access port. Drove 20 miles and its pending but hasnt set. Went back to work cleaned the MAF Sensor.Cleared it again and now pending. Have been looking for vacuum leaks none found.

Current mods:

gfb bov set to 50/50
Turbo back exhaust
Deastchwerks fuel pump
Aem Cai
2009 sti w/ 36k miles
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Old 10-08-2013, 01:20 PM   #555
Scooby Specialist
Member#: 289514
Join Date: Jul 2011
Chapter/Region: South East
Location: Jax, FL
2003 WRX Sedan
Ralley Blue


The cai can cause it, as well as exhaust leaks.
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Old 10-14-2013, 02:01 AM   #556
Scooby Newbie
Member#: 360519
Join Date: Jun 2013
Location: Central Valley, CALi
2002 Impreza wrx
Midnight black pearl


My P0171 goes on and stays off for about 200 miles sometimes more than comes back on.
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Old 12-05-2013, 11:30 PM   #557
Scooby Newbie
Member#: 375426
Join Date: Dec 2013
Location: Utah
2005 Legacy GT

Default Thanks a bunch

I created a profile on this site so I could say thanks. I appreciate the time you took to share your learning for the benefit of others.

In case anybody was wondering all the same goes for the Legacy GT. Here's my P0171 story. About three weeks ago I got a P0171 and checked all the easy culprits. Vacuum Hoses, filter box, visual checked the MAF sensor. The next day my radiator exploded on the freeway (completely unrelated, I assume), and while I had things apart I again checked all the hoses I could find, and even bought some MAF cleaner and drowned the sensor.
After changing the radiator out the CEL went away for a couple of weeks. Then, the day after Thanksgiving I was headed down the freeway and noticed that my instantaneous MPG reading was 4 to 6 MPG low. I went for about 40 or 50 miles that way before the CEL came back. I racked my brain and nearly exhausted my google searching ability before I came across this thread.
After checking most all the other options I concluded that it must be the O2 sensor. I don't have a Subaru buddy that I can swap parts out with (My little brother with a Leggy GT lives in Cali) so I took a chance and bought the part on Amazon. As of a few days later all seems to be normal, fuel economy has returned to normal, and I'm happy.

Thanks again for your thread. Much appreciated.

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Old 02-21-2014, 05:21 PM   #558
Scooby Specialist
Member#: 109567
Join Date: Mar 2006
Location: Qatar

So I have a cel on my 07 sti about 2 days ago.

I left home to work and it was perfectly fine. Then when I started my car again to get back home, I just noticed that the way my engine sounded is not as before and somehow my afr gauge showing 16~16.5 !!! drove the car slowly and when cruising my afr is perfect (14.5 to 14.9) yet no cel.

Then when I reached home cel came on, and my car idel is hunting a little bit! afr were 16~16.5 and when I blip the throttle it pick up rpm normally, but then gose all the way down to 300~200 rpm for 1 sec then back to 900 rpm.

so bad o2 sensor is ruled out as what I think its functioning correctly, because I have external arf gauge.
vaccum reading at idel fluctuatuing between 18.75~18.9 inHG
fuel pump, spark plugs, injectors (denso 1000cc) are new with less than 1500 miles

one thing before this P0171 cel, that I was trying to solve rich afr reading at wot I do hit target boost (too slow at ~ 5000 rpm) and my afr become rich past 4500 rpm giving reading of 9.5~9.6
its boost leak issue but just want to share the history

anyway what to look for solving P0171?
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Old 06-06-2014, 09:53 AM   #559
Scooby Newbie
Member#: 352421
Join Date: Apr 2013
Chapter/Region: South East
Location: Italy
2006 wrx tr
obsydian black bedliner


Ive done everything, tried new pumps checked for exhausts and intake leaks changed my fuel pump and filter changed both my afr and 02 sensor and maf sensor and still nothing. l cant log my wideband because a pin broke out so i have to fix that. But narrow band reads rich when cruising and lean when accelerating and the car pops and bucks really bad. Car has vf48, full catless turbo back and 2 in up pipe, 825cc modded stock injectors, perrin turbo intake pipe with hks filter, hks ssqv bov, and tgvs deleted. It was tuned in texas 3 years ago and ive had it in italy for a year and the code just started this past sunday after a 3 hour drive.
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Old 06-06-2014, 09:58 AM   #560
Scooby Newbie
Member#: 388099
Join Date: Apr 2014
2005 WRX


I've been fighting with this code for about a month now. I thought it may have been an o2 sensor and I get that replaced but the CEL still came back. I suspect it could be my short ram intake could be causing it since I haven't gotten a tune for it.

The only mods I have for it are catback exhaust, the short ram, and an up pipe. Any suggestions on what it could be? I'm going to try to remove the short ram this weekend and replace it with a stock airbox to see if that makes it go away.
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Old 06-06-2014, 10:00 AM   #561
1 sic 04wagon
Scooby Newbie
Member#: 359712
Join Date: Jun 2013
Chapter/Region: SCIC
Location: Cali
04 Wrx wagon
Metallic Silver


Boost leak , bov not seating. , there r two wires deep inside the mag that require attention sparky cleaner in there and let sit. Do not emerge sensor in fluid that's a quick way to kill it
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Old 08-21-2014, 02:47 AM   #562
Scooby Newbie
Member#: 399510
Join Date: Aug 2014

So I am having this problem on my mothers 06 legacy gt. Ive checked the vacuum hoses, sprayed the intake manifold down with carb choke cleaner to find any leaks and nothing. Also cleaned the MAF and my parents have ran 2 tanks of injector cleaner and still having issues. Car will buck on light acceleration between 2500 and 3000 rpms...I threw it on a snap on diag tool. What are the o2 readings supposed to be? Im getting 2.7ish volts on one and .8 on the other...any help would be much appreciated.
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Old 08-24-2014, 05:08 PM   #563
Scooby Newbie
Member#: 398998
Join Date: Aug 2014
Chapter/Region: NESIC
Location: Massachusetts
05 92x aero


The fix for my PO171 cel, was replacing the maf meter. I checked everything, also cleaned the old maf meter a couple of times. Code always came back, But replacing it,
did it.
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Old 09-30-2014, 08:05 PM   #564
Scooby Newbie
Member#: 364543
Join Date: Aug 2013
Location: Pennsylvania
'08 WRX Sedan


Great post! I removed my CAI and connected a PVC pipe with an industrial air fitting. I then hooked it up an air compressor with 20 psi and instantly heard a leak by my innercooler. Ended up being the coupler between the innercooler and intake manifold. I bought a perrin silicon coupler to fix it.
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Old 10-15-2014, 12:09 PM   #565
Scooby Newbie
Member#: 397216
Join Date: Jul 2014
Location: Rochester NY, Boston MA
2002 WRX

Default ECU too

Had a p0171 code with PFFFE for multiple misfires recently. Turned out that the ECU had gone bad, causing a misfiring issue.
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