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.
Reading codes properly on a Toyota
A £20 reader pulls generic engine codes and nothing else. On a Toyota the useful information often sits in the gearbox, ABS, body or comfort modules, and those need a tool that talks the manufacturer protocols. Just as important is the freeze-frame data stored with the code: engine speed, load, coolant temperature and fuel trims at the exact moment the fault was logged. That snapshot is usually what separates a failing sensor from a real mechanical problem, and it is the first thing we look at before anything is unbolted.
Why the same code costs different money on a Toyota
Each code on this page has a cost range rather than a price because the cheap cause and the expensive cause log identically. A split hose and a failed turbo can both set a boost code. Access matters too — some Toyota engines put the awkward part behind half the front end, and the labour, not the part, is what moves the bill. An honest quote names which cause has been confirmed and what the repair for that specific cause costs.
Getting a Toyota fault diagnosed
Bob's Mechanical Repairs is an independent, family-run garage in Birnam, Dunkeld, Perthshire, a couple of minutes off the A9. Bob has 32 years on the tools, and diagnostics are charged as diagnostic time with the findings explained in plain English and the repair priced before any work is agreed. An MOT is £54.85 if the car is due one at the same time.
Common questions
How do I read fault codes on a Toyota? Any generic OBD-II reader will pull engine codes from a Toyota built after 2001, but manufacturer-level codes from the gearbox, ABS and body modules need a tool that speaks the Toyota protocols. That is why a garage scan often finds codes a cheap reader misses.
Will clearing a Toyota fault code fix it? No. Clearing the code only erases the record. If the fault is still present it returns on the next drive cycle, and in the meantime the readiness monitors are reset, which can stop the car passing an emissions check.
How much is a Toyota diagnostic at an independent garage? An hour of diagnostic time is typically £50–£90 in the UK, against £110–£180 at a main dealer. It almost always costs less than the part it stops you buying by mistake.