Subaru - Repeat Fault P2096

Bill Owner/Technician Jackson, Michigan Posted   Latest   Edited  
Question
Driveability
2011 Subaru Outback 2.5i 2.5L (EJ253) (TR690)—4S4BRCCC2B3325607
P2096 - Post Catalyst Fuel Trim System Too Lean Bank 1

This issue has gone on too long! use to be 10-20K before fault would reset now its about 3K. Freeze frame data always indicates a proper fuel trim +/-5% . when driving vehicle trims are always good to.. This fault has occurred 5 times in 35,000 miles now! 

We have replaced the front A/F sensor 2 times and rear oxygen sensor 1 time. I have smoked tested the exhaust system cold - no leaks can be found. Vehicle is in very good condition and well cared for. I do not find related TSB or re flash information regarding this fault. Looking for some advise what am i missing here??

I have attached the most recent freeze frame data 

diag​.​net/file/f1w3d37yr…

+1
Randy Diagnostician
Glendora, California
Randy
 

I have fixed this code on other manufactures by doing ecm reset and erase all learned values. Have not done this on subaru

+2 Ð Bounty Awarded
Chad Owner/Technician
Perth, Australia
Chad
 

It's interesting looking at your freeze frame particularly b1s2, reading .825v when the fault occured, that's Rich not lean? Strange it set a lean code. Anyway I have experienced on some vehicles. Again not Subaru, injectors causing this code. The thing was looking at fuel trim and freeze frame data everything looked ok, had plus or minus 5 short term and plus 2 or 3 long term. I couldn't…

+2 Ð Bounty Awarded
Richard Technician
Virginia Beach, Virginia
Richard
 

First thing I start with is reading ALL mode 6 data.

0 Ð Bounty Awarded
Bob Owner/Technician
East Longmeadow, Massachusetts
Bob
 

Bill, I have found that smoke testing the exhaust is not always effective at finding small leaks. I would suggest putting pressurized air into the tailpipe and then use soapy water to test for leaks. Just like you would test for a tire leak. This method will find tiny leaks that cause these O2 codes.

+7 Ð Bounty Awarded
Michael Owner/Technician
Salt Lake City, Utah
Michael
 

Have you checked with Subaru for an updated sensor with a PCM reprogram or a TSB? I recall this occurring on earlier models with an A/F Sensor.

0 Ð Bounty Awarded
Chris Diagnostician
Bryans Road, Maryland
Chris
 

I don’t have very much info in fixing this problem but I like to do a little googling of the forums some times when weird problems like this occur. Seems like there is about 10-15 ones I found that match your case. Most of them have all been to dealer with just parts throw at them because nothing shows up during testing. None of the members on the forums had said anything about the dealers…

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Maynard Technician
Elmira, Ontario
Maynard
 

Does it still have original Cats on it? I was helping a guy work on a Saturn once with this, we fixed up all kinds of very small exhaust leaks and we made sure software was up to date etc, but it had an aftermarket cat welded in. There was no efficiency codes set, just the 2096. The way the car was eventually "fixed" was to weld in an additional small body cat in front of the existing one. Light…

+2 Ð Bounty Awarded
Bill Owner/Technician
Jackson, Michigan
Bill
 

Here is the mode 6 data. diag​.​net/file/f2risizaq… ​ Vehicle has OE / original converter on it never have had a efficiency fault. We have been servicing this vehicle for +100,000 miles. When smoke testing the exhaust we do it cold / vehicle sits all night exhaust is filled using smoke machine then shop air is used to push the smoke. at a previous visit the battery cables were…

0 Ð Bounty Awarded
Richard Technician
Virginia Beach, Virginia
Richard
 

I do not see anything wrong so thanks for posting this. I think many people forget about this info. By memory , i believe the rear O2 usually sits at about .680 under normal conditions .

0 Ð Bounty Awarded
Bob Owner/Technician
East Longmeadow, Massachusetts
Bob
 

Bill, use soap solution on the exhaust. Many times you cannot see the smoke coming from very small leaks.

+3 Ð Bounty Awarded
Hollis Technician
Boulder, Colorado
Hollis
 

Reverse Blow Shop Vac Method ? Thanks to Trained by Techs, saw their video on this method.

+1 Ð Bounty Awarded
Bob Owner/Technician
East Longmeadow, Massachusetts
Bob
 

I use a regulated blow gun through an inflatable block off tool in the tailpipe. I believe I did first see this technique through trained by techs.

0 Ð Bounty Awarded
Hollis Technician
Boulder, Colorado
Hollis
 

Check this out: *** Control the sub feedback learning and judge as NG when the learning value is in the lean zone.*** I believe this references the B1S2 STFT, yours is -3.1% in the freeze frame. IIRC 0.0% is normal. ***Setting conditions*** Engine running in Closed Loop; amount of intake air more than 1.0 kg, vehicle speed more than 50 mph, and the PCM detected that the HO2S signal did not…

+1 Ð Bounty Awarded
Randy Analyst
Denver, Colorado
Randy
 

I have not diagnosed that DTC on that model of vehicle so I don't have any specific insight. However, I do get quite a few calls on these DTCs so I can give you a clearer understanding of what is going on. P2096,P2097, P2098 and P2099 are much misunderstood. They are intended to reflect rear o2 or sub o2 fuel correction issues. Subaru uses a sliding mode controller type fuel control that…

+8 Ð Bounty Awarded
Jason Owner/Technician
San Luis Obispo, California
Jason
 

Since this has been a reoccurring problem you may want to move forward with replacing the complete exhaust manifold. This design is not very good. You can get a aftermarket one very reasonably.

0 Ð Bounty Awarded
Hollis Technician
Boulder, Colorado
Hollis
 

Thanks for the explanation Randy, it adds to and confirms my suspicions and assumptions based on limited experience of what's actually going on with these codes. It's definitely not a single test drive scan/graph session, more of a multiple test drives, lengthy testing, inspecting and a process of elimination, just shy of shot-gunning questionable aged sensors based on accumulated mileage and…

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Leo Technician
Rhinebeck, New York
Leo
 

Have you used OEM sensors every time? I see this code often, and 99% of the time, it is due to either the AFR sensor or the O2 sensor being unable to "see" either a rich or lean condition. Randy's post is very enlightening, because the freeze frame data frequently indicates the opposite of the code description! So, thanks Randy, now we know why! I find that one of many skills we need as…

+3 Ð Bounty Awarded
Hollis Technician
Boulder, Colorado
Hollis
 

…gt;forget "too lean" or "too rich" That's it !!! Excesses in the FT's for the P2096 as compared to say setting / enabling conditions for a P0171 are a lot less and the time frame for it as well. Comparing the Detecting Criteria between the two codes is the difference between Main Feedback and Sub Feedback. We're accustom to the term 'too rich or lean' meaning as we all know as an excess of…

+1 Ð Bounty Awarded
Randy Analyst
Denver, Colorado
Randy
 

These DTCs were developed around the … time frame and the reason for them was that a large number of engine/exhaust designs did not do a very good job of measuring lambda on each cylinder. Everything worked fine on a perfectly balanced, new engine but as things fail, systems could not see issues. There were engines that you could disconnect injectors and the front exhaust sensor never…

+4 Ð Bounty Awarded
Hollis Technician
Boulder, Colorado
Hollis
 

Thanks, I'm starting to build a picture here and see what you're saying. I've been trying to familiarize myself with Lambda, slow going... They do list Imbalance DTC's for this year model, but it's for the 2.5 DOHC and not the SOHC. Hmmm ???? Detecting Criteria includes Low-Count Misfires... As for exhaust manifold design, this seems to fit Subaru's redesigned version that appeared in 2005…

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Sean Technician
Forest Lake, Minnesota
Sean
 

Fantastic information. Thank you for sharing

0 Ð Bounty Awarded
Hollis Technician
Boulder, Colorado
Hollis
 

Don't know if 'I ' actually shared any real or useful information, more just thinking out loud, Glad you enjoyed it. I think the combination of shared info, especially from those In-The-Know is what makes the whole topic interesting and gives us a little more insight as to the nature of the issues we face in the automotive world and the answers to the mysteries we seek. Kinda like once you…

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Bill Owner/Technician
Jackson, Michigan
Bill
 

Thank you guys so much for all of your help, information and time!! Lots of good stuff here! I gave the vehicle back to the owner for a bit but I have surly not given up... I think I need to get the heat shields off the front pipes/ convertors (Michigan car ☹️) and then use the soapy water method to eliminate any possibility of a leak. The sensors previously replaced we're Denso brand.

0 Ð Bounty Awarded
Hollis Technician
Boulder, Colorado
Hollis
 

Before you pull the rusted exhaust manifold down, give the bubble test to the manifold gaskets. See attached image. By the time I could take the picture the bubbles had dissipated, needed 3 hands. but IIRC this Subaru had a P0171, this leak was relatively small, not audible cold or hot, no carbon residue. Graphing while driving prior to replacing the gaskets, the fuel trims were going…

+1 Ð Bounty Awarded