Fault code

P0304 fault code.

This code comes up with 2 known faults.

Generic code

Code type

Engine and drivetrain

System

Misfire on cylinder 4

The engine control unit detects a misfire from the momentary slowdown of the crankshaft, and tied this one to cylinder 4. An ignition coil, a spark plug, an injector or a leak can all cause it. The repair is often a new spark plug or a new ignition coil.

The code tells you what the control unit measured, not which part has failed. The same code has several possible causes.

Which known faults it comes up with

expensive1

FSI direct injection: intake valve coking

expensive

With direct injection the fuel does not wash the intake valves: the petrol goes into the cylinder, not behind the valve. The oil mist and soot arriving through the EGR and the crankcase ventilation therefore build up on the valve stem and head, and from 80,000 to 100,000 km they restrict the flow. Symptoms are hesitation, loss of power, a rough cold start and misfire. It is not a part failure: it is a consequence of the design, and therefore it comes back. Cleaning (walnut or dry ice blasting) helps for a few tens of thousands of kilometres.

What to check

After a cold start watch the idle: rough running and shaking point to coked valves
Under load at low revs watch for hesitation
With a code reader look for per cylinder misfire (P0300 to P0304)

1 more steps in the write-up

cheap repair1

TSI ignition coil: misfire, jerking, engine warning light

cheap repair

The per cylinder ignition coil of these direct injection, turbocharged petrol engines fails. According to the Haynes service material this and similar simple electrical faults account for roughly eighty per cent of workshop visits.

Show the rest

In cold, damp weather, on startup, the engine runs unevenly, misfires under acceleration, and the engine warning light flashes or stays on. Do not keep driving with the light flashing: the unburnt fuel destroys the catalytic converter.

What to check

Start with a cold engine and watch the first half minute: a rough idle or shaking is suspect
On the test drive load the engine at low revs with a lot of throttle: the misfire shows then
A flashing engine warning light calls for stopping immediately

2 more steps in the write-up

Information, not an expert opinion

We write the descriptions, and we put the source next to them. A person reviews them before they go out. They are still information, not a technical expert opinion.

A fault on the list does not mean the car you are looking at has it.
A fault missing from the list does not mean the model is fault-free. Write-ups are made model by model. Not all of them are done.
You decide whether to buy. This is no substitute for an inspection. That needs a workshop and a history check.

Details in the terms