P0420 on Ford TDCi – Catalyst / DPF Efficiency

Platform‑specific notes for dealing with P0420 on Ford TDCi and EcoBlue diesel engines.

What P0420 Means on a Diesel Ford

On many Ford diesels, P0420 is effectively complaining that the after‑treatment system (oxidation catalyst and/or DPF) is not performing as expected. It may appear alongside DPF pressure or temperature‑related codes.

Common TDCi‑Specific Causes

  • DPF that has been heavily overloaded or has a history of incomplete regenerations.
  • Temperature or pressure sensors giving incorrect readings to the ECU.
  • Physically modified or removed DPF/catalyst hardware.
  • Long‑term EGR issues leading to abnormal soot loading patterns.

Suggested Test Plan

  1. Read out DPF soot load, ash load and regeneration counters with a capable scan tool.
  2. Inspect exhaust temperature and pressure sensor readings for plausibility.
  3. Confirm the presence and condition of the DPF and catalyst hardware.
  4. Investigate any related EGR or boost‑control codes before condemning the DPF/cat.