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Discussion Starter · #1 ·
So as the title says, my wrx has had this issue since I drove it home from out of state, was about a 250-300 mile commute. It all started after getting gas on my way home. I had a code reader, plugged it in, and had pending codes p0420 p0137 p2096 and a rare occurrence of p2196. all of these codes, aside from p0420 are straight up O2 sensor codes, but p0420 is a cat code.. The issue i’m having is none of these codes actually pop up as a CEL, some days they are there pending, and some days they don’t even show, so I can’t get it diagnosed as they are not true, active DTCs. I notice no performance problems, other than a little performance lag in the warmer weather, but I feel that is normal when it is 105 degrees in arizona, and I usually don’t push the car hard, never have even put it close to redline.. My question is, since they aren’t active DTCs, will they cause more harm to components? I plan on taking it in immediately as they do show up, but as of now, nothing pops on the dash. Should I be good to go until they actually show up?
 

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If I recall, and its been a while, a downpipe installed without a tune or a tune installed for an aftermarket downpipe will cause a series of codes similar to what you have. I'm not 100% on the bottom side of the VA chassis so I can't visually say the entire thing you have photos of is stock but I'm not familiar with an aftermarket unit with a flex installed.

If I were diagnosing this on my car I would suspect the cat or rear O2
 

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Discussion Starter · #7 ·
If I recall, and its been a while, a downpipe installed without a tune or a tune installed for an aftermarket downpipe will cause a series of codes similar to what you have. I'm not 100% on the bottom side of the VA chassis so I can't visually say the entire thing you have photos of is stock but I'm not familiar with an aftermarket unit with a flex installed.

If I were diagnosing this on my car I would suspect the cat or rear O2
That’s what I was thinking, probably an O2 sensor on the verge of dying, as all of the codes are related to that area. If the codes aren’t popping up constantly, or actually popping the CEL, is it okay to drive with them just while pending until I can take it with a code to get a proper diagnosis?
 

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Compare stock pics to your car and figure out what's modified or not. That downpipe definitely looks aftermarket and I've never seen the underside of a VA WRX.
 

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Discussion Starter · #9 ·
Compare stock pics to your car and figure out what's modified or not. That downpipe definitely looks aftermarket and I've never seen the underside of a VA WRX.
well, i jinxed it, drove tonight and the check engine light popped on with p0420 as a 2/3 severity… Can I continue to drive it? Doesn’t feel like any drivability issues, and it will be getting taken in, but for the time being do you think it’s okay to drive?
 

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Discussion Starter · #11 ·
The whole thing is aftermarket for sure. I'll post what pics I have of VA underside. I was taking pictures of other things so none of them really focus on exhaust.
hmmmmm… thank you for those pics. very strange. Well I know now that the exhaust is aftermarket, and upon further investigation, I have realized that my J pipe does looks to be catless, is that what could be causing my codes? How do I permanently fix this so that I can pass emissions and not continually have these O2 sensor codes, and this 0420 code that actually popped my engine light on? Is reverting to oem my best option?
 

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Depends on your end goals. If you are happy with stock power then yes oem catalysts will give you the most reliable setup. If you plan on increasing power signicantly, you can look for a tuner who will tune for j-pipes and a make a list of other upgrades. There are some aftermarket j-pipes with enough catalyst efficiency to not throw codes. Be aware they won't pass inspection if your state does visual like CARB.
 

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Discussion Starter · #13 ·
Depends on your end goals. If you are happy with stock power then yes oem catalysts will give you the most reliable setup. If you plan on increasing power signicantly, you can look for a tuner who will tune for j-pipes and a make a list of other upgrades. There are some aftermarket j-pipes with enough catalyst efficiency to not throw codes. Be aware they won't pass inspection if your state does visual like CARB.
my end goal is reliability. I am completely content with a subarus stock power, and just want it to run properly with no headaches in the long run. I was unaware of the exhaust when I bought the vehicle(as I bought it from a dealer who got it as a trade in from a guy who got a golf r) Do you know where I can find a full OEM exhaust system? I’ve been looking, but can’t find the entire thing.
 

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Discussion Starter · #14 ·
Depends on your end goals. If you are happy with stock power then yes oem catalysts will give you the most reliable setup. If you plan on increasing power signicantly, you can look for a tuner who will tune for j-pipes and a make a list of other upgrades. There are some aftermarket j-pipes with enough catalyst efficiency to not throw codes. Be aware they won't pass inspection if your state does visual like CARB.
Would I need a tune if I got a catted J pipe?
 

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Oem tune for oem j-pipe, custom tune and the added cost of an accessport if you get any other catted j-pipe.

Try to get in touch with previous owner, either thru dealer or some other way. Often some upgrades/mods/problems are hidden and talking to previous owner gives you a lot of information about the car and how it was treated.

Mostly subaru dealers for oem j-pipe, look up pqrt numbers and prices on parts.subaru.com. Nasioc, this site and other forums will have used j-pipes for sale occasionally from people who upgrade. It will be rare since this gen is not in production anymore.

For the rest of the exhaust, stock exhaust and the upgraded sti exhaust for fa20 are close in price and might be a worthwhile upgrade. There are also a bunch of nice aftermarket exhausts like the the invidia r400(a bit loud) or q300 (a bit quieter but hangs a bit below bumper)
 

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Discussion Starter · #16 ·
Oem tune for oem j-pipe, custom tune and the added cost of an accessport if you get any other catted j-pipe.

Try to get in touch with previous owner, either thru dealer or some other way. Often some upgrades/mods/problems are hidden and talking to previous owner gives you a lot of information about the car and how it was treated.

Mostly subaru dealers for oem j-pipe, look up pqrt numbers and prices on parts.subaru.com. Nasioc, this site and other forums will have used j-pipes for sale occasionally from people who upgrade. It will be rare since this gen is not in production anymore.

For the rest of the exhaust, stock exhaust and the upgraded sti exhaust for fa20 are close in price and might be a worthwhile upgrade. There are also a bunch of nice aftermarket exhausts like the the invidia r400(a bit loud) or q300 (a bit quieter but hangs a bit below bumper)
If i went with an oem up pipe, and an upgraded down pipe/intermediate pipe, would I need a tune? Can I go back to a stock tune after all of this has already been done?
 

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Your post says wrx, not sti. Your are confusing different engines here. Up/downpipe on ej series engines only, i.e. STi. WRX, i.e. FA20 engine has a j-pipe with 2 catalysts. And yes if you keep all oem catalysts you can keep stock tune.
 

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Discussion Starter · #18 ·
Your post says wrx, not sti. Your are confusing different engines here. Up/downpipe on ej series engines only, i.e. STi. WRX, i.e. FA20 engine has a j-pipe with 2 catalysts. And yes if you keep all oem catalysts you can keep stock tune.
My apologies, did not know the wrx and sri were that much different, yeah, my J pipe does not have a cat. There are 2 o2 sensors, that are supposed to be on each side of the cat, but where those are, there is no cat, in the photos I posted above, Is that a cat near my control arms? Or is in a resonator?
 

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Discussion Starter · #19 ·
Your post says wrx, not sti. Your are confusing different engines here. Up/downpipe on ej series engines only, i.e. STi. WRX, i.e. FA20 engine has a j-pipe with 2 catalysts. And yes if you keep all oem catalysts you can keep stock tune.
I am trying to get ahold of the previous owner, because I am sure he has a tune on it, with my peak boost saying 23.5 when the boost on OEM WRX is around 15.9 correct?
 

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Can't say what it is from outside pics. You either need confirmation from prev owner or remove it to look inside. Either way if it's throwing efficiency codes then it's not good enough.

16psi steady boost pressure but it spikes to 21-24psi at the start when you floor it.
 
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