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Old 10-16-2019, 10:31 PM   #1
Scooby Newbie
Member#: 507475
Join Date: Oct 2019
Default 2010 Impreza P0420

Whats up all,

long time browser first time poster, i know there are many posts on this yet mine is different from all i have read.

Here are the facts:
2010 impreza 5 speed, rebuilt motor and swapped trans 5000 on engine and 100k on trans, 150k body (paperwork inc)
Have aftermarket cat/exhaust manifold.
Have a P0420 code and a permanent CEL, No TCS, No Cruise (as of today)

I was driving this morning and the car studered for about 10 seconds at a stop light. A few miles later it stuttered then went into limp mode for roughly a minute throwing the CEL, blinking Cruise, and no TCS. I drove it about another 4 miles to my destination. Got it scanned and popped a P0420. Drove her home and the lights are constant but no more limp, in fact it feels perfect except the lights. The exhaust looks fine no cracks, loose bits or otherwise.

Its $260 for both sensors, although i know it could be the cat. I feel like my gas mileage is pretty crappy currently.

Should i jimmy the sensors to rid the codes or spend money on a whole new setup? any advice would be helpful i'm in a tight spot for money until november.

Here's a few pics, first is cat/manifold second is connection post cat and third is connection post mid pipe.



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Old 10-17-2019, 12:39 PM   #2
Scooby Newbie
Member#: 491095
Join Date: Sep 2018
Chapter/Region: SWIC
Location: New Mexico
2009 STi Blue


that code directly suggests the cat...if you want more proof get a laser temp sensor and measure temp before and after cat(after running it like you are goin to an emission test)...if its stupid hot then its clogged..if its normal operation then its the sensors
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Old 10-17-2019, 03:29 PM   #3
Add Lightness
Member#: 13699
Join Date: Dec 2001
Chapter/Region: NESIC
Location: Hopkinton, MA
not my president
(From General)


P0420 means "I'm a Subaru". At least that's how I decode it.

You can try all the tricks out there. But if you're having actual drivability issues, have a mechanic who knows what he's doing look at the signals from the front and back O2 sensors. It might be the cat. It might not.
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