What does this code mean?
The controller judged catalyst performance below its threshold under the monitor's test conditions. P0420 refers to bank 1 and P0430 to bank 2. Inspect exhaust leaks and related misfire or mixture codes; assess sensor signals and the vehicle-specific catalyst test. The code alone does not prove the catalyst or an oxygen sensor needs replacement.
Sources and interpretation [1]
A code identifies a detected condition, not a part that must automatically be replaced.
Manufacturer communications
9Original wording in English
HONDA
Reported code forms P0420
Dealer Message - American Honda Motor Co., Inc. (AHM) is searching for certain 2018-2024 Accord 1.5Ls, 2021-2024 Civics 1.5Ls, 2023-2024 CR-Vs 1.5Ls, and 2017 Fits with customer complaint of Check Engine Light (CEL) on…
HONDA
Reported code forms P0420
Dealer Message - American Honda Motor Co., Inc. (AHM) is searching for certain 2018-2024 Accord 1.5Ls, 2021-2024 Civics 1.5Ls, 2023-2024 CR-Vs 1.5Ls, and 2017 Fits with customer complaint of Check Engine Light (CEL) on…
HONDA
Reported code forms P0420
PRODUCT UPDATE: ECM UPDATE TO PREVENT CATALYST DTC P0420 AND/OR VPS DTC P1021, MCM UPDATE TO CURRENT SPECIFICATIONS. *TT
HONDA
Reported code forms P0420
MALFUNCTION INDICATOR LAMP ON WITH DIAGNOSTIC TROUBLE CODE P0420 OR ENGINE PING UNDER LOAD. *TT
HONDA
Reported code forms P0420
REPLACE THE CORRECT THREE WAY CATALYTIC CONVERTER FOR DTC P0420 P01420 P2000. *EH
HONDA
Reported code forms P0420
DIAGNOSTIC TROUBLE CODE P0420 AND P1420 REPAIRS. *TT
Check vehicle applicability
14A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.
| Make | Model | Model year |
|---|---|---|
| Honda | CIVIC | 2024 |
| Honda | CIVIC | 2023 |
| Honda | CIVIC | 2022 |
| Honda | CIVIC | 2021 |
| Honda | CIVIC | 2005 |
| Honda | CIVIC | 2004 |
| Honda | CIVIC | 2003 |
| Honda | CIVIC | 2002 |
| Honda | CIVIC | 2001 |
| Honda | CIVIC | 2000 |
| Honda | CIVIC | 1999 |
| Honda | CIVIC | 1998 |
Before replacing a part
Record codes and freeze-frame data. Check battery condition, related codes and visible wiring or hose damage. Follow the vehicle's diagnostic procedure and test results before replacing parts.
Sources and interpretation
These explanations are editorial summaries of the linked manufacturer material. PDF page numbers count from the first file page. Original publications are in English; translations are reference aids. A cited edition is not a claim that it is the manufacturer's latest instruction.
- 2024–2025 MY OBD System Operation Summary for Gasoline Engines ↗
Ford Motor Company · PDF page(s) 2, 3 ·
Source check date · 2026-10-27
Can I keep driving?
A code alone cannot establish whether driving is safe. A flashing malfunction light, severe shaking, overheating, oil-pressure warning or loss of braking or steering needs prompt attention. Stop in a safe place and seek assistance when control or engine safety is affected. Follow the vehicle handbook.