Cylinder 4 misfire on Audi — VAG TSI/TFSI coil failure, 2.0 TDI injector or glow plug, plus carbon-fouled plugs on 2.0 TFSI EA113.
Audi P0304 — Cylinder 4 misfire on Audi — VAG TSI/TFSI coil failure, 2.0 TDI injector or glow plug, plus carbon-fouled plugs on 2.0 TFSI EA113. Typical UK independent garage cost: £120–£720.
What actually causes P0304 on a Audi
Audi shares VAG TSI coil failure with VW — cyl 4 first on EA113 and EA888 engines. EA113 2.0 TFSI additionally suffers carbon-fouled plugs from direct injection — plug life is barely 30k miles. On 2.0 TDI CR Audis cyl 4 misfire is usually injector or glow plug. 3.0 TDI V6 Audi cyl 4 misfire is rarer but when seen, almost always injector.
Audi engines that log P0304
- 2.0 TFSI EA113 (A3, A4 B7, S3 8P)
- 2.0 TFSI EA888 (A4 B8, A5, A6, Q5)
- 2.0 TDI CR (A3, A4, A6, Q5)
- 3.0 TDI V6 (A4, A6, Q5)
How we diagnose P0304 on a Audi
- VCDS — read per-cylinder misfire counters
- Swap coil 4 to another cylinder
- Pull all 4 plugs (replace if over 30k on EA113 TFSI)
- On 2.0 TDI, glow plug test and smooth-running values
- Walnut blast intake if heavy carbon
The common misdiagnosis to avoid
On Audi 2.0 TFSI EA113 with cyl 4 misfire, replace ALL 4 spark plugs (£35 of plugs) AND swap the bad coil — the other plugs will be at end of life regardless.
Audi P0304 repair cost in the UK
Expect £120–£720 including parts and labour at an independent garage. Main-dealer quotes on Audi 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
Always quote a walnut blast alongside coil/plug work on EA113 2.0 TFSI — the customer pays once and the engine actually runs properly afterwards. Doing the coils without the carbon clean fixes the code but leaves the engine running 30 HP down.
Codes usually seen alongside P0304 on Audi
- 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 Audi 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 Audi 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 Audi'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 Audi, 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.