What Toyota codes (P0420, P0301, P0171, P0304, P0011, P0299) actually mean on Toyota engines — the real cause, the common misdiagnosis, and the honest UK repair cost.
These are the OBD fault codes we see most often on Toyota vehicles in the workshop, with the real cause on Toyota engines rather than the generic textbook definition, plus the honest independent-garage cost.
Toyota fault codes explained
- P0420 — Toyota P0420 (Catalyst System Efficiency Below Threshold, Bank 1) is the single most-searched Toyota fault code in the UK — and on Yaris, Auris, Corolla, C-HR and Prius it splits three ways: genuine cat wear at 120,000+ miles, a tired rear (downstream) lambda sensor that mimics cat failure, or straight catalytic-converter theft. Toyota hybrids remain the #1 stolen-cat target in Britain according to the AA and every major insurer. Typical UK cost £300–£1500.
- P0301 — Cylinder 1 misfire on Toyota — usually coil pack on 1.8 VVT-i / 2.0 D-4D, but on the 1.4 D-4D injector failure is very common. Typical UK cost £50–£1200.
- P0171 — System too lean (Bank 1) on Toyota — MAF sensor, intake gasket and PCV are the common UK culprits on 1.8 VVT-i and 2.0 VVT-i. Typical UK cost £40–£600.
- P0304 — Cylinder 4 misfire on Toyota — coil pack failure on Yaris/Auris/Corolla 1.0/1.3/1.4 VVT-i; plug condition on hybrid Prius/Auris. Typical UK cost £80–£380.
- P0011 — VVT-i over-advanced on Toyota 1ZZ/2AZ/2GR — the OCV filter clogs with sludge from extended oil changes. Typical UK cost £140–£600.
- P0299 — Turbo underboost on Toyota — 2.0/2.2 D-4D and 1.2T Yaris/Auris hybrid turbo charge-pipe and actuator issues. Typical UK cost £180–£1400.
- P0016 — Crank/cam correlation Bank 1 on Toyota — 1.2T 8NR-FTS chain stretch and 2.0 8AR-FTS VVT-iE actuator. Typical UK cost £180–£1800.
- P0455 — EVAP gross leak on Toyota — fuel cap and vacuum switching valve on Corolla/Yaris/Auris. Typical UK cost £20–£280.
- P0410 — Secondary air injection malfunction on Toyota — 4.7 V8 (Land Cruiser) SAI pump and switching valve. Typical UK cost £240–£1400.
- P0341 — Camshaft position sensor performance on Toyota — VVT-i 2ZR/8AR sensor and OCV (oil control valve). Typical UK cost £100–£380.
Codes are generic across manufacturers, but the fix is not. The same code on a Toyota 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.