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2006 Outback 2.5i Auto
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417 Posts
Discussion Starter #1
I've had an intermittent P2097 "post Cat too rich b2" code on my Outback for the past couple of weeks. An ECU reset has got rid of it for a few drives, but they've mostly been too short to bring it up to full temperature and it may not have gone to the closed loop operation in that time (it's cold here and full temp takes several miles to reach). I understand from searching here that either pre or post-Cat O2/AFR sensor failing could trigger the error.

I've replaced the air-filter and cleaned the MAF, as the filter was just about due, which got rid of the CEL for a week or so. So right now I'm assuming that one of the two original O2 sensors (123k miles, non-Cal car) is fading out, but I can't tell which one with FreeSSM/RomRaider. What are the expected voltages in closed loop, fully up to temperature operation for the two sensors? Is that the best way to diagnose?
 

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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16,144 Posts
@plain OM you are up ... he'll have the goods for you.
 

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03 H6 OBW & 06 WRX Sportwagon
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17,704 Posts
how's the exhaust system? any chance of a leak?
 

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2005 Outback Wagon with 2.5L NA Auto
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46 Posts
I'm having a similar issue. http://www.subaruoutback.org/forums/109-gen-3-2005-2009/460457-cel-p2097-code.html

Would be nice to know what voltages the front O2 sensor should provide open loop/closed loop. I haven't had time to dig that information out. Also, what should the MAF be reporting in grams per second? FWIW, I had to replace my front O2 sensor around 140,000 miles. I don't think it's bad after two years and I'm having similar issues. I'll be following your post to see what you find out.
 

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2006 Outback 2.5i Auto
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417 Posts
Discussion Starter #5
how's the exhaust system? any chance of a leak?
Nothing's been touched there, so yeah, there's chances of a leak but no specific reason to suspect one. The timing is plausible for an O2 sensor failure, I think.
 

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2006 Outback 2.5i Auto
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417 Posts
Discussion Starter #6
By the way. I now have the 2005 complete FSM, with the DTC diagnosis tree that gives voltages for that year. Don't have it for 2006 though, and I don't know if anything changed there.
 

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2006 Outback 2.5i Auto
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417 Posts
Discussion Starter #7
Following the FSM that I was kindly provided with by plain OM, I tracked it down to the AFR/Front O2 sensor.

Diagnosis was basically "is there a good voltage at the rear sensor (0.8V at idle when warmed up)" followed by letting the rpm drop from 3k and watching the rear O2 sensor drop to zero before returning to the 0.8V.

New one has just gone in, in 15 degree weather, using the loaner tools from Advance Auto. Pulling the air intake made it easily doable with the 7/8" crow foot, a 3/8" to 1/2" adapter, wobbler, 6" extension and 12" extension coming up between the P/S pump and the coolant hose, and a breaker bar.

The sensor was covered in carbon when I got it out, indicating that the car's been running very rich for a while.

Now I just need to fix the incontinent power steering, which isn't liking the cold weather.
 

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2006 Outback 2.5i Auto
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417 Posts
Discussion Starter #8
Power steering now fixed with the usual 65¢ 1/2" ID, 5/8" OD, 1/16" wall O-ring from the hardware store and bit of ATF fluid.
 
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