P0420 on Subaru vehicles The catalytic converter on bank 1 is not cleaning up the exhaust as well as it should
P0420 is named on 46 Subaru model years (2016–2023): 100 manufacturer filings and 2 owner reports in NHTSA’s files, across Legacy/Outback, WRX, Forester, Ascent, Crosstrek and 3 more.
Which Subaru model years name P0420
Source: NHTSA manufacturer communications and complaintsA model year is listed because the code is named in its own record — a bulletin filed against it, or an owner’s complaint about it — not because every one of these vehicles sets it. Counts are documents in NHTSA’s files, not failure rates.
Subaru filings that name P0420
Source: NHTSA manufacturer communicationsBulletins and campaigns Subaru filed with NHTSA whose summary names P0420. Quote the document number at the service desk — it is a diagnosis the maker has already written down.
- 09-110-23 Service bulletin2023-10-09 · Engine And Engine Cooling
- This Service Information Bulletin announces diagnostic service procedures to be followed when DTC P0420 (Catalyst System Efficiency Below Threshold Bank 1) is detected by the Engine Control Module (ECM). If DTC P0420 is found to be stored in the ECM, follow the diagnostic procedures outlined below.
- 09-110-23R Service bulletin2023-11-07 · Equipment
- This Service Information Bulletin announces diagnostic service procedures to be followed when DTC P0420 (Catalyst System Efficiency Below Threshold Bank 1) is detected by the Engine Control Module (ECM).
- 09-131-25R Service bulletin2025-08-11 · Engine
- This bulletin announces the diagnostic procedures and availability of reprograming files to rectify the following Diagnostic Trouble Codes (DTCs). • P2404: EVAP System Leak Detection Pump Sense Circuit Range/Performance. • P0420: Catalyst System Efficiency Below Threshold Bank 1. (not applicable for 15-18 models)
- 09-131-25 Service bulletin2025-03-04 · Electrical System
- "This bulletin announces the diagnostic procedures and availability of reprograming files to rectify the following Diagnostic Trouble Codes (DTCs). • P2404: EVAP System Leak Detection Pump Sense Circuit Range/Performance. • P0420: Catalyst System Efficiency Below Threshold Bank 1. (not applicable for 15-18 models)"
- 09-131-25 Service bulletin2025-04-08 · Engine
- This bulletin announces the diagnostic procedures and availability of reprograming files to rectify the following Diagnostic Trouble Codes (DTCs). The ELCM may accumulate condensation causing the inaccurate detection of P2404. P0420 may become falsely detected due to unstable combustion caused by a downshift. The new reprogramming files contains enhanced software allowing for condensation conditio
What P0420 means
Source: SAE J2012 / OBD-IIThe catalytic converter on bank 1 is not cleaning up the exhaust as well as it should.
A stored code names the test that failed, never the part that caused it. The record above is what Subaru and its owners have filed about it; the code’s page across every make has the whole file.
Common questions
Source: NHTSA files and the OBD-II standardIs P0420 a known problem on Subaru vehicles?
It is a documented one: NHTSA's files hold 100 manufacturer filings and 2 owner reports naming P0420 on 46 Subaru model years (2016–2023). Whether it is a problem on one particular car is a diagnosis, not a count — but a bulletin that names the code on your model year is the place to start.
Which Subaru models does P0420 appear on most?
2017 Legacy/Outback (4 documents), 2021 WRX (4 documents), 2020 WRX (4 documents).
Does P0420 on a Subaru mean it is recalled?
No. Recalls are filed by campaign and matched by VIN; no recall is triggered by a scan tool. Check the VIN at nhtsa.gov/recalls, or open the model year's page here for the campaigns filed against it.