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Guest Message by DevFuse

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2009 Forester Code P2097, bad fuel economy, replaced both O2 Sensors, what now?

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7 replies to this topic

#1 dmcclosk531


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Posted 08 January 2013 - 11:06 AM

Hello All,

I'm new to the forum, and to Subaru ownership. I picked up a 2009 Forester SOHC, 5 speed, now with 65,000 miles. When new to me the car regularly got 27-28 MPG on the highway going 70mph.

Over the last month or two i noticed it slipping to 25-24-23, then one day the CEL came on, traction control light came on, and cruise control shut off and started flashing.

Got the code checked and cleared with the following results " P2097 Post catalyst fuel trim system too rich bank 1 confirmed" drove the car for approximately 100 miles, with fuel economy around 20mpg highway and then the light came back on, same code. So, i replaced the post catalyst O2 sensor. Drove another 100 miles or so, light came back on. This time i replaced the pre-cat upstream O2 sensor. (also changed the air filter while i was in there)

I haven't driven the 100 or so miles it seems to take the CEL to come back on, but judging by the fuel economy, around 20mpg highway, its only a matter of time and i have not fixed the underlying problem.

Any ideas what other systems or sensors might be causing this issue?
The car other wise runs, drives, idles, and starts normally. Power seems normal. perhaps a little bit of stutter when starting from a stop, but i might be imagining it. it's very slight if anything at all. might just be my clutch action....

Thanks for any help or ideas. I'll update again when/if CEL comes back on.

#2 grossgary


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Posted 08 January 2013 - 11:26 AM

Hopefully someone a little more versed in this steps in as this sounds fairly abnormal for any Subaru particularly this low mileage.

I wonder if one of the fuel injectors may be leaking too much fuel into the cylinders.

Is it ever hard to start?

Fuel injectors aren't hard at all to replace so don't let it scare you. It is very rare for them to fail so even a low mileage used one is a reasonable fit particularly for one this new. Sometimes new prices are a bit absurd for parts that rarely fail.

They can also be cleaned/tested/rebuilt by RC Engineering or Witchhunter

But again hopefully someone can offer some specific testing/symptoms/suggestions to narrow it down for sure.

#3 dmcclosk531


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Posted 08 January 2013 - 12:25 PM

I ran a bottle of fuel injector cleaner through, didn't see any change. Haven't looked into the injectors any further than that.

#4 dmcclosk531


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Posted 08 January 2013 - 12:37 PM

Always seems to start easily

#5 ShawnW


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Posted 09 January 2013 - 03:57 AM

How old are the spark plugs?

#6 dmcclosk531


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Posted 09 January 2013 - 09:07 AM

Not sure, bought the car used and haven't changed them

#7 GeneralDisorder


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Posted 09 January 2013 - 11:16 AM

You should change the plugs - air filter too if you haven't.

After that if things don't improve then you need to hook into the live data and do a sanity check on what's coming from things like the coolant temp sensor, MAP sensor, and MAF/IAT sensors. The mixture is too rich and the ECU's fuel trim routines think everything is ok because one of its sensors is out of calibration - that would be my guess.


#8 russerts



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Posted 29 June 2013 - 10:50 AM

I just encountered this problem last night on my 2012 Forester (24k miles). CEL, Traction Control light, and flashing Cruise light.  I stepped on the throttle to pass a truck at 50 mph with four passengers on board and got this as I accelerated - right after it downshifted.  I have not checked the codes yet but this certainly seems like a specific, though odd, set of indications. I don't know whether there is any effect on mileage because I was only 50 miles from home.

Edited by russerts, 29 June 2013 - 10:51 AM.

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