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2004 Subaru Forester XT
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Discussion Starter · #1 ·
First post here. I know there’s many threads regarding o2 sensors and whatnot but I can’t seem to find exactly what I’m looking for.

My CEL is on with code P0134 - O2 circuit no activity detected (bank 1, sensor 1)

I know I need to replace the o2 sensor 1 (air/fuel sensor). I have the part and also the ratchet tool. I’m having trouble figuring out where it is on my Invidia exhaust system. I have an Invidia g200 catback with an Invidia catted downpipe.

I can see a sensor right underneath the car on the passenger side right after the oil pan. I also see one inside the engine bay looks like it’s attached to the manifold. They both look like they are before the cat so I’m a bit confused. I’ve scoured the internet for help but I want to be sure. Any help would be greatly appreciated. Thanks!
 

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2004 Forester XT Auto
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317 Posts
From the service manual DTC codes, the sensors are "BANK 1 SENSOR 1" and "BANK 1 SENSOR 2". Therefore, BANK 1 SENSOR 1 would be the O2 sensor in the uppipe (engine bay). SENSOR 2 is after the downpipe cat, typically called the "downstream" O2 sensor. I believe the 04-05 foresters actually have 3 cats in total, one in the uppipe, one in the downpipe, and one in the midpipe. On later cars the uppipe cat was deleted due its tendency to kill turbos.
 

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2004 Subaru Forester XT
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9 Posts
Discussion Starter · #3 ·
@Galaxywide Thanks for your input! Much appreciated! The O2 sensor has came in I’ll be installing tomorrow.
 
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