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.
Toyota 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 independent garage cost: £80–£380.
What actually causes P0304 on a Toyota
Toyota coil packs are generally robust but failures do occur by 100k miles — Yaris/Aygo small engines especially. On 1.8 hybrid (Prius/Auris) cyl 4 misfire is almost always a spark plug at end of life (90k–100k mile service interval) or a cracked porcelain insulator from over-torquing during a DIY plug change. 1.4 D-4D diesel cyl 4 misfire is glow plug or injector.
Toyota engines that log P0304
- 1.0/1.3 VVT-i (Yaris, Aygo)
- 1.33 Dual VVT-i (Yaris, Auris)
- 1.4 D-4D diesel (Auris, Avensis)
- 1.8 hybrid (Prius, Auris, C-HR)
How we diagnose P0304 on a Toyota
- Techstream — read per-cylinder misfire counter
- Pull spark plug 4 first — inspect for wear, oil fouling, cracked porcelain
- Swap coil 4 with another cylinder if plug looks OK
- On 1.4 D-4D, glow plug test
- Replace component, road-test (hybrids: be aware of regen behaviour after fault clear)
The common misdiagnosis to avoid
Don't immediately quote a coil on a hybrid Prius/Auris with cyl 4 misfire — pull the plug first. 80% of the time it's a worn or cracked plug, and OE Denso plugs are £15 each.
Toyota P0304 repair cost in the UK
Expect £80–£380 including parts and labour at an independent garage. Main-dealer quotes on Toyota are usually higher for the same job, and the spread exists because the cheap cause and the expensive cause throw the same code — pay for the diagnosis before you pay for parts.
Bob's workshop tip
On Prius/Auris hybrid plug changes, always torque to spec (16–22 Nm) with a proper torque wrench — over-tightening cracks the porcelain and you'll be back fitting plugs in 30k miles instead of 100k.
Codes usually seen alongside P0304 on Toyota
- P0300
- P0301
- P0302
- P0303
Symptoms drivers report with P0304
- Engine warning light flashing (not steady) under load
- Noticeable juddering at idle in gear
- Smell of unburnt fuel from the exhaust
- Misfire worse when engine is cold and damp
- Significantly reduced power
Repairs that clear P0304
- Plug & coil replacement
For the generic, all-makes explanation of this code — meaning, every known cause and UK cost bands — see our P0304 guide.