Live Data
Last reported case: 1 weeks ago
Based on 7 owner reports (7 from Reddit)
What is P0420?
🚗P0420 on 2020 SUBARU WRX
This page focuses specifically on P0420 issues reported by 2020 SUBARU WRX owners. The experiences and fixes below are from real owners of this exact vehicle.
Parts Often Involved:
dashrear o2exhaust manifolds
What Owners Say
Real experiences from 2020 SUBARU WRX owners
Experiencevia reddit_post
“Can ROMRAIDER populate and ECUTEK tune if plugged into the OBD? So essentially I have a stage 2 tune with a catted invidia downpipe and I get the P0420 code.”View original
Experiencevia reddit_post
“So essentially I have a stage 2 tune with a catted invidia downpipe and I get the P0420 code. This is going to be an issue to pass emissions inspection in my new area.”View original
Experiencevia reddit_comment
“snitch o2 is so accurate. i have a p0420 and i tried spacing the rear o2 and it just swapped the p0420 with a p0137 lmao”View original
Experiencevia reddit_comment
“my condolences, i currently have had a p0420 for 2 years and i’ve done everything i could to address it”View original
Cost Reportvia reddit_post
“Aftermarket j pipe+ tune - $1,910 I mean I feel like there really is only one choice here, an this might be the easiest upgrade to convince the MOF of, since I need my CEL off to pass inspections”View original
Experiencevia reddit_post
“I got walnut blasted a couple months ago and ever since then I’ve had a constant p0420 coming up. Finally had time to take it into a Subaru dealership and they asked if they took the exhaust manifolds off to walnut blast, I said I don’t think so.”View original
Experiencevia reddit_post
“I assume this caused the issue finally got around to scanning it, and nothing except for a pending p0420 (which I can attribute to the aftermarket catted dp, tuner must've set it to stay in pending instead of not checking cat at all)”View original
Experiencevia reddit_post
“Hill Assist Failure Light on, no codes A while ago the hill assist light came on while slowing to turn, but never braked enough for the assist to come on.”View original
These are real experiences shared by 2020 SUBARU WRX owners on automotive forums and communities. Results may vary based on vehicle condition and repair quality.
About This Data
This page aggregates 7 discussions about P0420 from 2020 SUBARU WRX owners across automotive communities.
Success rate (0%) is calculated from posts where owners confirmed whether their fix resolved the issue.
Last updated: 1/12/2026