2021 Hyundai P0304: What It Means & Is It Safe to Drive?
P0304 on the 2021 Hyundai: Cylinder 4 Misfire Detected. Here's what it means, what usually causes it, what repairs typically cost, and whether it's safe to keep driving.
PowertrainHigh urgency
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 on the 2021 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 2021 Hyundai, repairs for P0304 typically fall between $150 and $900, depending on the root cause and labor rates in your area.
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
Sonata 2.4L GDI 2011–2019Elantra 2.0L GDI 2011–2016Tucson 2.0L 2016–2020