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Old 01-08-2019, 12:51 PM   #27
Scooby Newbie
Member#: 496174
Join Date: Jan 2019
Location: Downers Grove, Illinois
2000 Impreza OBS

Default Double code p0420, 267k miles, 2000 OBS

Background Info:
2000 Impreza OBS(manual), two owners(including me), well maintained and (almost always) serviced on time. 267k miles and everything is stock/original to the car minus the scheduled replacement parts and a swapped throttle body from a 1999 Impreza 2.2l (down pipe sprung a leak causing overheating and the "new" throttle body only cost around $70). Not much of a car guy, but I'm learning.

I was late on my oil change this time (life happens) and I had just replaced my knock sensor for the code I was throwing originally. My inspection is this month and on my way to the state facility, my check engine light comes on. I go to auto-zone to get them to read the code for me and they tell me "The code is p0420 which is your catalytic converter. It's showing up twice.". Knowing very little about cars, I take to the internet for research.
After about a half an hour of reading, I feel like my worst nightmare has been realized and I have to replace the whole cat and possibly my whole exhaust. But then I take to the forums here and find a whole slew of information.

Solution (so far):
I waited until my gas tank was close to empty, put in catalytic converter cleaner (Redline) and drove (agressively on the highway/slow and steady around town) until I had to refuel. Filled up the tank and then dumped in a whole can of seafoam. I did some more highway driving (including 3 distinct pulls from 30mph to 80mph) and then around town driving like a "sensible grandpa". I returned home for several hours and, from a cold start, drove down a road that had intermittent stop lights every 4 or 5 miles with an average speed limit of 45-50mph for about an hour. When I woke up this morning and went to start Lucy Sue the Subaru to warm her up, no more codes. Checked in with auto-zone as well and they confirmed no codes.

I'm not sure if this is going to last longer than a day or two or if I'm actually in the clear, but I do hope this was helpful to someone.

P.S. definitely replacing the entire exhaust soon. Exhaust front to back is all original and truth be told, that kind of scares me haha.
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