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Old 05-28-2019, 02:19 PM   #1
Kanchou
Scooby Newbie
 
Member#: 46936
Join Date: Nov 2003
Location: Atlanta
Vehicle:
2004 WRX

Default ap for cel diagnostics

Got a V3 form my 04 wrx, no recent changes to car, started throwing p0171, but no performance hit is noticed.

can the AP help me diagnose more accurately where I need to look? ( i have the p0171 thread queued up in another tab, but if this can tell me more then id like to know)
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Last edited by Kanchou; 05-28-2019 at 03:20 PM.
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Old 06-10-2019, 04:50 PM   #2
Justorymes
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Member#: 502897
Join Date: Jun 2019
Location: SouthEast Wisconsin
Vehicle:
2006 Impreza WRX
Black

Default

an P0171 should be Fuel Trim system Lean Bank 1. Our cars seem to be very prone to vacuum leaks that may cause this lean condition.

On the Accessport you can monitor your Short and Long term Fuel trim's, they are labeled "A/F Correction #1" and "A/F Learn".
After the vehicle is warmed up take it for a cruise (Freeway will be good). If the "Fuel Learn" Perameter passes +15% it will set this DTC.

If this is the condition your experiencing I would suggest looking for a vacuum leak after the Mass Air Flow Sensor and but before the cylinder head. The intake manifold gaskets are very common also so you might have some luck starting there. You can also get this code from an exhaust leak at the manifold, so don't eliminate that right away.
Smoke testing the intake is the safest way to perform this test but most people don't have access to EVAP leak tester that I happen to use personally, you can always use short burst's of brake clean while the engine is running on the problem area(s) in question and monitor the "A/F Correction" change then you will have found your leak.

Other common things are forgetting to attach something after you have worked on the vehicle, such as the Recirculation hose, EBC hose, EVAP hose, or PCV hose. Don't forget to check your boost guage and line/fittings if you are using an auxiliary one.

Just some ideas to try.
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