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Old 01-23-2007, 01:41 PM   #76
thejean
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Join Date: Apr 2002
Chapter/Region: W. Canada
Location: Calgary, AB
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Check the intake manifold... I had a blown hose on my EGR valve. Got the CEL under vacuum.
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Old 01-23-2007, 02:29 PM   #77
MidRex
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Location: Pittsburgh
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2007 STI (Sold)
03 WRX FP Green PPG (RIP)

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I'm wondering if the front O2 could possibly throw P0172 also. I've checked everything else and still get it.
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Old 01-23-2007, 02:57 PM   #78
thejean
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Yes it can.
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Old 01-23-2007, 03:14 PM   #79
MidRex
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03 WRX FP Green PPG (RIP)

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I was wondering because it doesn't seem to matter what I do with my tune (UTEC). Even if I leave the ECU in control up to 50% TPS, I still get the code. I guess you get it when you max out your trims to LTFT -25%.
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Old 03-22-2007, 06:21 PM   #80
anthonyrb98
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Chapter/Region: SCIC
Location: san diego
Vehicle:
02 bugeye
hbspeed tuned 18g sleeper

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bump for more info!
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Old 05-17-2007, 09:08 PM   #81
probot757
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Chapter/Region: South East
Location: Panama city beach , Fl
Vehicle:
2015 WRX
WRB

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Thanks for the excellant write up. I just got my scooby wagon and it is already throwing this code. I was about to smash my head into a brick wall, but now I have a general direction to work with. Thanks again..
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Old 05-18-2007, 10:11 AM   #82
CirrusWRX
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Location: Yardley, PA
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2002 x2 Silver WRX
Sedan, White WRX Wagon

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Yeah unfortunately there are a LOT of general directions and it can be a royal PITA tracking these buggers down, but at least a majority of them don't cost much money if anything at all, but they do cost time.

Good luck! As always, please post up your results if you find anything in the list or anything not already in the list.
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Old 07-02-2007, 12:04 PM   #83
Vinnyzwrx
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Chapter/Region: TXIC
Location: Grand Prairie, TX
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2014 STI
WR Blue

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nice thread
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Old 07-05-2007, 01:27 PM   #84
scoob-noob
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Thumbs up Thank You, Thank You, Thank You!!!

First want to thank everybody in this community, it really feels like Subaru owners very genuine people.

If you don't want to read my ranting just skip to the last paragraph.

Thanks PAWRX & CirrusWRX, i've been wrestling with the P0171 issue for almost a year now. Before the CEL P0171 first came on I brought my 03' WRX in to the Subaru shop to get another CEL resolved. My Subaru mechanic replaced a fuel sensor on top of my fuel tank. About a month later I get a CEL and my car was driving real sluggish with very choppy acceleration above 3500 rpm. I brought my car back in and they told me I needed a new fuel pump which will run me $600 for them to do it - they diagnosed low fuel pressure. So I decided to replace it myself. I replace my fuel pump with a Walbro 255 - same price as factory replacement, oh and by the way, very very easy. First time doing anything really mechanical to my car. 30 miles later the CEL comes back on. I was confused because my car felt normal. Extremely pissed because it felt like my Mech sabotaged my car. I've drove my car with the CEL on for a while because I had no time, I was very busy at work. I search the web on P0171 CEL and came across this thread. Found it on pure dumb luck reading various other miss-informed threads which had me change my fuel filter (which I know is part of regular maintenance). For real I agree this Thread should be a Sticky.

To Shorten my story, reading the 2nd billet of PAWRX & CirrusWRX check list, I checked my factory intake box and noticed one of the insert lip on my bottom part of the box (the part where you slip in the top part of the box where there are no clips) had broken off. Luckily there was an '07 factory intake box for sale on ebay for $45. The Subaru parts guy will tell you he doesn't know if the '07 will fit the '03, but for $45 compared to $275 I just bought it. It fits just fine, one small issue. The screw holes for the MAF sensor on the '07 Intake are just drilled holes. I stripped the threading because the '03 had metal nuts molded into the mounting and so I was twisting for a firm screw-in. With a new intake system I've been driving CEL free for over 400 miles.
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Old 11-09-2007, 08:23 PM   #85
ddub22
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Just threw code P0171 after cleaning my MAF sensor. I had the code come on before and I thought it was because of my Oil filter, so I cleaned the MAF. Now the car idles rough, as if it is misfiring or bogging down.
- checked all connections, even took off the IC to make sure hoses are tight. Put a extra hose clamp on the BOV recirc into intake
- checked all vacuum lines
- put silicone around the MAF to make sure it wasn't a seal leak
- cleaned the O2 sensor
- Bought a new MAF sensor

Still idleing rough and throwing the code. The car does drive fine, just idles like crap then throws the code. I reset the ecu a bunch of times already and checked to make sure its running the correct base map.

I didn't check the IACV, what would have changed by cleaning the MAF sensor??? Any suggestions???

Car is 2004 wrx, stg 2 AP, short ram intake, cated dp, gruppe-s headers, hoses.
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Old 11-09-2007, 09:25 PM   #86
Vinnyzwrx
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Location: Grand Prairie, TX
Vehicle:
2014 STI
WR Blue

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try turning the maf around 180 degrees, sometimes its easy to put the maf in backwards if you have an aftermarket intake that looks ths same backwards.

if the maf is in backwards it would do everything that your saying that its doing.
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Old 11-09-2007, 11:15 PM   #87
ddub22
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Just checked, the MAF is in the right direction. Just had my buddy who is a mechanic check the hoses, everything seems normal. All the conditions point to a vacuum leak, but can't find any leaks. Any other suggestions??
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Old 11-10-2007, 06:20 PM   #88
blahhblahh
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2005 WRX Sedan
WR Blue

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would an exhaust leak, pre-02 sensor cause this cel. i belive i have an exhaust leak since its pretty damn loud now, and I get this code.
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Old 11-11-2007, 11:50 AM   #89
20BlueWRX02
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Chapter/Region: MWSOC
Location: Midland, MI
Vehicle:
2006 WRX Limited
WRB

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I've been getting this P0171 code like all the rest of us here and the car seems to idle fine, drive fine and if it weren't for the light I really wouldn't notice anything abnormal at all.

My question is: what is the sensor that comes out of the uppipe? The reason I ask is because a few months back I did the up/down pipe install myself and I plugged the bung with a bolt and used the 2.2k resistor mod. Well earlier this morning it hit me and I assumed that might have been the front O2 sensor that was talked about here(then agian it could be the one in the headers too...I think there was one there) Anyway, I went out and checked the resistor and sure enough one end had fallen out of the connector. I replaced it and re-taped it back up good. I reset the code using my AP and took a short drive (less than 5 miles) and no light so far.

Somebody who knows, could this have been the issue? I sure hope so!
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Old 11-12-2007, 02:07 PM   #90
PAWRX
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Location: Dublin, PA
Vehicle:
2002 slvr wrx sedan
07 CBR 600RR

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Yeh, the resistor was most likely the problem. The sensor in the uppipe is the EGT. The sensor in the header is the front O2
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Old 12-14-2007, 05:49 PM   #91
CyaWRX
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Location: Alexandria VA
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2005 WRX
Black

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wow thanks this is going to come in handy seeing as how my cel came up with the P0171 code
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Old 01-07-2008, 11:26 AM   #92
ride5000
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2003 GGA MBP
12.9 / 105+

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Quote:
Originally Posted by blahhblahh View Post
would an exhaust leak, pre-02 sensor cause this cel. i belive i have an exhaust leak since its pretty damn loud now, and I get this code.
yes, it could, especially at idle and low tps (where backpressure is low).
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Old 01-07-2008, 10:16 PM   #93
wrblueballs
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Join Date: Jul 2006
Chapter/Region: MWSOC
Location: Independence/Cincinnati
Vehicle:
2005 WRX 20G, PPG
WRB

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nice write-up. i now have a direction to go! i'm running a stage four system on my 05 and after i first got tuned, i threw this code. took it back, they said it kicked out my base map and reloaded the realtime. no problems for almost a year, but just last week the cel came back on and the thing has a super rough idle and stalls out when coming to a stop. it's really aggravated the mortal crap out of me...
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Old 01-07-2008, 10:57 PM   #94
bluesubywagon
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2004 wrx sti wagon
blue

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Hi. I had a similar problem. It was the intake. My bet would be that the MAF calibration is at the border line with the new short ram. With mine I noticed that as soon as the weather cooled down it stopped happening. In the warm weather it had the same symtoms. Mine was a custom calibration that over time the ecu learned from the O2 sensor to a point that every now and then it was out of the O2 sensors range of keeping the ecu happy. Hope this helps!
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Old 01-12-2008, 09:33 PM   #95
txl146
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Chapter/Region: Tri-State
Location: NY
Vehicle:
02 WRX VF34
Junior Tuned 301whp

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this should be sticky.... very nice information here.
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Old 01-12-2008, 09:41 PM   #96
wrxrex
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Vehicle:
Old Stage 4 bugeye

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guys, if P0171 light came on 30 miles after replacing a fuel filter, what can be wrong? I made it sure it's installed properly and there isn't anything I can think of that can cause CEL.

1. MAF sensor - cleaned and checked.
2. Very smooth idle and drivability
3. No sign of knock (data log done using enginuity)
4. IACV cleaned and new gasket installed 5k miles ago
5. Intake box is sealed well.
6. Fuel injector cleaner and fresh tank of 93 gas

This leaves me with two possibilities - bad O2 sensor or defective fuel filter purchased from autozone. Are there anything else I should be looking at? I just placed an order for a new O2 sensor ($160 shipped).

Thanks guys...

Last edited by wrxrex; 01-13-2008 at 01:48 AM.
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Old 01-13-2008, 01:49 AM   #97
wrxrex
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Old Stage 4 bugeye

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I also tried both K&N panel filter and paper filter. P0171 light is still on. I'm running out of idea here. Maybe I should try another fuel filter.
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Old 02-13-2008, 09:25 PM   #98
Rodwrx23
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Location: Pembroke Pines, FL
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Hey guys. I've been having this code too for about a month now. After reading the suggestions I've
1. Cleaned my filter on my Perrin Big MAF
2. Cleaned my MAF sensor and replaced the o-ring
3. cleaned my IACV and replaced my gasket
4. replaced my rear 02 sensor after also throwing P0137
5. I have also used fuel injector cleaner/octane booster and ran 110 unleaded
6. I've tried looking for leaks and cracked or loose hoses and can't really find any
7. I have a 2.2k resistor in my uppipe plug and my UTEC logs also say I'm running rich.

I'm really banging my head against the wall and don't know what else to look for.
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Old 03-03-2008, 02:01 AM   #99
justinh595
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I'm throwing this code on my 02.
setup:
hks catback
3'' downpipe catless
catless uppipe
cobb ap stage 2
stock intake etc

i've run through the list and haven't had any luck so far. replaced front o2 sensor and still no luck.
The car idles/runs fine...the only thing i notice is poor gas mileage. The only thing i can think of is i may have bumped something doing a trans about a month ago..the code has been coming on since about that time. I've checked everything in that general area (pulled ic etc) thinking i may have bumped something while working but came up with nothing obvious. Also the trans i replaced mine with is out of an 04 which shouldn't effect that but maybe someone knows something i don't. any suggestions?
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Old 03-10-2008, 10:56 AM   #100
maengelito
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Chapter/Region: MAIC
Location: Charlottesville, VA - MM
Vehicle:
2005 Forester XT

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Quote:
Originally Posted by Speedinticket View Post
Bumping an old thread.... I just popped this code yesterday. After reading this thread, I found that the airbox wasnt sealed. I reset the computer, and that's the last I saw of it.

Thanks for the help!
i know this particular post is over a year old, but if the airbox isnt properly sealed, will the car still idle fine? one of the plastic tabs that you slide the upper part of the intake box into broke off but the car idles perfectly.
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