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
13Original wording in English
CADILLAC, CHEVROLET, GMC
Reported code forms P0420
This Preliminary Information communication provides information to the technician on the steps to diagnose and repair vehicles that may have a Service Engine Soon Malfunction Indicator Lamp on at low mileage. Technician…
CADILLAC, CHEVROLET, GMC, HUMMER
Reported code forms P0420
This Preliminary Information communication provides information to the technician on the steps to diagnose and repair vehicles that may have a Service Engine Soon Malfunction Indicator Lamp on at low mileage. Technician…
CHEVROLET, GMC
Reported code forms P0420
This Preliminary Information communication provides information to the technician of additional information while diagnosing a diagnostic trouble code P0420. Check for a possible leak in the exhaust system behind the…
CHEVROLET, GMC
Reported code forms P0420
This Preliminary Information communication provides information to the technician with additional information while diagnosing a diagnostic trouble code P0420. Check for a possible leak in the exhaust system behind the…
CHEVROLET, GMC
Reported code forms P0420
This Preliminary Information communication provides information to the technician about vehicles that have a Malfunction Indicator Lamp on. Technician may find a P0420, P24A0 and/or P2463 set. Technician should use…
CHEVROLET, GMC
Reported code forms P0420
This Preliminary Information communication provides information to the technician about vehicles that have a Malfunction Indicator Lamp on. Technician may find a P0420, P24A0 and/or P2463 set. Technician should use…
Check vehicle applicability
17A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.
| Make | Model | Model year |
|---|---|---|
| Chevrolet | EXPRESS | 2018 |
| Chevrolet | EXPRESS | 2017 |
| Chevrolet | EXPRESS | 2016 |
| Chevrolet | EXPRESS | 2015 |
| Chevrolet | EXPRESS | 2014 |
| Chevrolet | EXPRESS | 2013 |
| Chevrolet | EXPRESS | 2012 |
| Chevrolet | EXPRESS | 2011 |
| Chevrolet | EXPRESS | 2010 |
| Chevrolet | EXPRESS | 2009 |
| Chevrolet | EXPRESS | 2008 |
| Chevrolet | EXPRESS | 2007 |
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.