P0420

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.

Original wording in English

A 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.

Scan worksheet →

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.

1. 2024–2025 MY OBD System Operation Summary for Gasoline Engines ↗

   Ford Motor Company · PDF page(s) 2, 3 · 2024-04-16

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.