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07 Forester XT Limited 4EAT
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Discussion Starter #1
I've had the P0171 code for a long time, the car basically runs fine, idle is fine, and it doesn't miss, but I generally don't push the car. The P0171 popped up a week or so after I got the secondary air valves and pump deleted (block off plates at the head), and the accompanying secondary air system codes removed. The P2096 showed up more recently, maybe the last month. I suspect an O2 sensor, a cat, or an exhaust leak. I checked my air box, ran a fuel system cleaner, and cleaned the MAF, but the codes persist. I have 115,000 miles on the car. If I get a chance I will use soapy water and spray bottle to look for exhaust leaks today. Can anyone suggest what else to look at? I was able to make a log today with a Tactrix 2.0 using the SD card, view it here: https://drive.google.com/open?id=0B9wxmOVRQOcXZk1BN0hVclBKbGc

Second question, how many catalytic converters are on this car after the turbo? I found this diagram of the exhaust http://estore.subarupartswarehouse.com/images/parts/subaru/fullsize/S11_44001329.png
Is there a cat on the downpipe, a cat next to where the O2 sensor plugs in, and ANOTHER car on the next intermediate pipe? They are labeled 44102B, 44102BA, and 44102BB in the diagram.
 

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2004 Forester XT 4EAT
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4102BB is the Resonator. So just "cat on the downpipe <and> a cat next to where the O2 sensor plugs in".

I'd replace the O2 sensor (use an Amazon or Ebay NGK part - or dealer if $$ is no object).

Or buy and 'anti-fouler' (extender) and see if that helps.

Otherwise, buy a Cobb (or similar) Catted DP to replace both of those others.
 

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2012 XT Touring 4EAT
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3,752 Posts
<snip>Second question, how many catalytic converters are on this car after the turbo?
In 2007, you should have one cat. The rear O2 sensor is located immediately behind it. You should not have catted up-pipes or down-pipes.

On the SAI delete, did you pull the fuses (and relay?) related to this system? I did a SAI delete a year or so back, but I did the lazy-man's version and left all the hardware in place but made sure the valves were closed before pulling the fuses. I deleted the codes. It's never so much as burped.
 

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07 Forester XT Limited 4EAT
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Discussion Starter #4
I had Precision Tuning do the SAI delete, I provided the kit from KS Tech that deletes the valves and pump, and blocks off the holes at the head. They removed the barometric pressure sensor from the one valve and zip tied it in the engine bay. Then they deleted the codes from the ECU. I dont know if they pulled any fuses or relays. Where would those be located? My valves were stuck open btw. I just brought the car in and had a smoke test done. He said there were no leaks, the codes were old and not current, sensor function and fuel trims looked good, so he cleared them. He said it might be an intermittent issue with the evap system. Does that sound logical?

I've reset the ECU by disconnecting the battery and hitting the brake pedal a ton of times, and the same CEL and codes always come back.
 

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07 Forester XT Limited 4EAT
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50 Posts
Discussion Starter #5
I replaced my front o2 sensor, and caulked up a spot that could possibly leak around the engine air filter box. I disconnected the battery, drove on the highway, turned off the car, drove again on the highway, and the CEL and blinking cruise came back on. I just went to pepboys to get the code checked again and it didnt show any codes stored in the ECU. Anyone have any ideas now? I have another appointment with Precision on Friday to see if they can diagnose what's going on.
 

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2012 XT Touring 4EAT
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I had Precision Tuning do the SAI delete, I provided the kit from KS Tech that deletes the valves and pump, and blocks off the holes at the head. They removed the barometric pressure sensor from the one valve and zip tied it in the engine bay. Then they deleted the codes from the ECU. I dont know if they pulled any fuses or relays. Where would those be located? <snip>
On my vehicle, there is an add-on fuse box, located in the engine compartment, next to the main fuse box. The relevant fuses/relays are in this add-on fuse box. They are marked as to what the do.

Disconnecting the battery to clear ECUO codes will work, but you had best leave the battery disconnected for 30 minutes or so. A more predictable way to do this is with an OBD-II reader/eraser.

Another responder mentioned an anti-fouler - usually called the $5 fix. The primary (only?) purpose of this mod is if you're getting "low cat efficiency" error codes. It's not a fix-all and I don't think it addresses any of the problems you're having. On the other hand, "low cat efficiency" codes are fairly common - ask me how I know ;-) - and the $5 fix did the trick. If you get the urge to replace O2 sensors, look on eBay for genuine Denso sensors. They can be had for $80 or less (front) and much less (rear). But the rear sensor is probably working - maybe working too well - which is why the $5 fix is useful. Basically, it desensitizes the rear O2 sensor.
 

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07 Forester XT Limited 4EAT
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Discussion Starter #7
See my last response right before yours. I got a Denso o2 sensor off amazon and replaced the old one, and the CEL came back. I read the ECU has some kind of diagnostic procedure where after a reset you have to drive the car 60mph for a little, park and shut it off, then drive 60mph again for it to complete it's diagnostics. Every time I do this, the CEL comes back on, but I went to pepboys to get the code scanned yesterday, and it didn't show any codes present. So now I have a CEL with no code.
 

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07 Forester XT Limited 4EAT
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Discussion Starter #8
Update: It was my mass air flow sensor. When I pulled the log myself the MAF reading wasn't fluctuating and I assumed it was working properly, but apparently the reading was off by a large increment overall and the ECU was unable to compensate. A new sensor and the car is running better than ever.
 
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