What does code P0304 mean on a Hyundai and is it safe to drive?
P0304: Cylinder 4 Misfire Detected. Here's what it means on your Hyundai, what usually causes it, what repairs typically cost, and how safe it is to keep driving.
What this code means
Misfire confirmed on cylinder 4. On 4-cylinder engines, this is the last cylinder—check coil and plug first, then injector, then compression.
Common causes for your Hyundai
- Worn spark plug on cylinder 4
- Failed ignition coil on cylinder 4
- Faulty or clogged fuel injector
- Low compression or valve issue
Symptoms
- Check Engine Light
- Rough idle and shaking
- Poor acceleration or power loss
Typical fixes
- Replace spark plug and COP coil on cylinder 4
- Clean or replace fuel injector
- Compression and leak-down test if basic parts check out
Repair cost range
For a Hyundai, repairs for P0304 often fall between $150 and $900, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on Hyundai
P0304 on Hyundai GDI four-cylinders follows the same carbon buildup pattern as other cylinders. On the 2.4L Theta-II, cylinder 4 is at the back of the engine and intake valve deposits here can be harder to reach during walnut blasting—ensure thorough cleaning.
Most commonly affected models