What Subaru codes (P0420) actually mean on Subaru engines — the real cause, the common misdiagnosis, and the honest UK repair cost.
These are the OBD fault codes we see most often on Subaru vehicles in the workshop, with the real cause on Subaru engines rather than the generic textbook definition, plus the honest independent-garage cost.
Subaru fault codes explained
- P0420 — Catalyst efficiency below threshold on Subaru — boxer engine cat failure from oil consumption and misfire history. Typical UK cost £400–£1600.
Codes are generic across manufacturers, but the fix is not. The same code on a Subaru usually points at a different component than it would on another make, which is why a make-specific diagnosis saves money before any parts are bought.