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2005 Outback 2.5i M
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Discussion Starter #1
Recently had a check engine light come on so I pulled the codes on my 2005 Subaru Outback (MT). I got P2097 and P0031. Yesterday and today, I had no problems driving the car until tonight coming home from work. It had a very hard time idling, nearly stalling a few times (I gave it more gas to keep it going). When warmed up, the problem seemed to go away.

Probably going to make time to go see a mechanic tomorrow, but just thought I'd post here to see if anyone had any thoughts.

P2097: Post Catalyst Fuel Trim System Too Rich Bank 1
P0031: Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)

I haven't had my injectors inspected in a long time. Maybe this is just a sensor though? Thanks in advance!
 

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2001 VDC/SC One of a Kind
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14,447 Posts
I'll give you a head's up. Do NOT let them replace the CAT. Repeat, DO NOT let them replace the CAT.

Diagnosis depends on whether your Outback is ULEV or base SOHC.

The P2097 needs to be ignored with the heater circuit code active. The rear O2 will send a rich value if the AF sensor is effecting fuel trim data that will cause the ECM to run rich. It could be a fault with another sensor on top of a failure in the AF.

Heater control circuit is most likely open in the AF sensor and is effecting the LTFT putting it in a rich zone which the CAT isn't able to keep up with. Most likely the data will show high negative STFT and LTFT numbers. The MAF sensor data needs to be varified as true, it may be sending low indicators.

List of possible replacement or cleanable parts: AF sensor 1/1 (if yours is ULEV bank one is the passenger side sensor), MAF sensor, PCV valve. The thermostat operation also needs to be checked.
 

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2005 Outback 2.5i M
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Discussion Starter #3
Really glad I posted. Thanks for the heads-up.

My OB is a base SOHC. 2.5L 4-cyl 5-speed Manual. What should I keep in mind with that information?
 

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2001 VDC/SC One of a Kind
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Most likely the front AF needs to be replaced. The MAF sensor output needs to be varified and clean the PCV valve and throttle body. After the repair, run High Octane gas and run a cleaner through the intake to remove carbon. It has most likely been running rich for a while. And check the thermostat operation. If a shop does the work, look towards a $300-400 bill. And don't let them condemn a MAF without proof. At running temp and idling 650-700 it should read 2.2-2.9 grams per second.

Run it on the highway often if you drive mostly short trips.
 

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2005 Outback 2.5i M
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Discussion Starter #5
Called me out on the short trips. Haven't taken it at highway speeds in a long, long time. Thanks for giving me an idea of what to expect. I'll post an update when I find out more!
 

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2005 Outback 2.5i M
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19 Posts
Discussion Starter #6
Just wanted to give the update:

It appears it was just the front a/f sensor. The shop I took it to charged me more than I think the sensor was worth, but replacing it seems to have fixed all of the problems!

I am currently running high octane and took it on a good highway trip as per cardoc's suggestion to help clean out carbon.

Thanks cardoc for your help! Do these forums have a reputation system? I can't seem to find where to upvote you.
 
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