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.
Reading P0304 on a Toyota properly
A generic reader will show P0304 and nothing else. What matters is the freeze-frame data stored with it — engine speed, load, coolant temperature and fuel trims at the moment the fault was logged — plus whether any other module on the Toyota has logged something at the same time. Codes rarely arrive alone, and the order they were stored in usually points at which one is the cause and which are the consequences.
Clearing P0304 without fixing it
Erasing the code resets the Toyota's readiness monitors as well as the light. The fault returns on the next drive cycle if the cause is still there, and in the meantime the incomplete monitors can stop the car passing an emissions check. After a genuine repair, the car is driven until the relevant monitor completes before it is handed back.
Bob's Mechanical Repairs is an independent garage in Birnam, Dunkeld, Perthshire, with 32 years of Bob's experience on the tools. If P0304 is showing on your Toyota, bring any scan results with you — we will read the live data ourselves, confirm which cause it actually is, and price the repair before any work starts.