P0420 on the 2021 Subaru WRX
The bulletins listed name this code in NHTSA's summary, or are about the same components. A bulletin or a recall listed here may apply to the model year. None of it is a diagnosis.
Nobody has written a description of this code yet.
| 09-131-25R | 2025-09-02. Service bulletin. 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 | 2025-05-01. Service bulletin. 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 conditions and downshift rotational speeds be more accurately detected by the Engine Control Module (ECM). |
| 09-131-25 | 2025-04-01. Service bulletin. "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)" |
| 09-110-23R | 2023-12-05. Service bulletin. 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). |
4 on file from NHTSA, as of 2026-10-19. See them in the bulletin list. A bulletin lists model years: read the document for which vehicles it concerns.