Ford P0420 — Meaning, Causes & Fixes

Guidance for the P0420 code on popular Ford vehicles like the F-150, Focus, and Escape.

Common Causes for a P0420 on a Ford

On many Ford models, a P0420 code is very frequently caused by a degraded catalytic converter. However, other issues are still possible.

Worn Catalytic Converter: The primary culprit on higher-mileage Fords.
Rear O2 Sensor Failure: A faulty downstream oxygen sensor can give false readings.
Exhaust Manifold Leaks: Cracked manifolds are a known issue on some Ford engines.