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 wording
Source wording can vary by vehicle and suffix. It is shown as written, not as a universal diagnosis.
P042000Catalyst System,Bank1 Efficiency Below Front window inoperative Air suspension warning - DTCP042000Catalyst System,Bank1 Efficiency Below"P042000Catalyst System,Bank1 Efficiency Below" Check engine lamp, Belt Starter Generator DTCManufacturer communications
3Original wording in English
AUDI
Reported code forms P042000
Noise from front door trim panel while driving Noise from front door trim panel while driving Low coolant warning in cluster, coolant level is correct Check engine lamp is on, DTC (s) P010600, P023600, P023700, P023800…
AUDI
Reported code forms P042000
Noise from front door trim panel while driving Low coolant warning in cluster, coolant level is correct Check engine lamp is on, DTC (s) P010600, P023600, P023700, P023800 Leak from oil pan USB Trim detached from center…
AUDI
Reported code forms P042000
3.0L engine sound generator malfunctioning Belt noise from starter generator Check engine lamp - DTC P240200 stored in ECM Check engine lamp is on, DTC (s) P010600, P023600, P023700, P023800 "Check engine lamp on, DTC…
Check vehicle applicability
3A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.
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.