P0304 on KIA OPTIMA — Cylinder 4 Misfire Detected

Q: "What does P0304 mean on a KIA OPTIMA?"

"P0304 indicates: Cylinder 4 Misfire Detected. This is a ignition system code. 4 KIA OPTIMA owners have reported this to NHTSA."

Q: "What are the most common causes of P0304 on KIA OPTIMA?"

"Based on 4 NHTSA reports, the most commonly cited components are: Engine, Engine,Fuel/Propulsion System, Power Train,Unknown Or Other,Engine. These percentages are based on the component field in owner complaints."

Q: "Is P0304 serious on my KIA OPTIMA?"

"Of 4 NHTSA reports for this code on KIA OPTIMA, none involved a crash or fire. However, any diagnostic code should be evaluated by a qualified mechanic."

Q: "What should I do if my KIA OPTIMA shows P0304?"

"1) Check for recalls on your VIN at nhtsa.gov/recalls. 2) Get a professional diagnosis — a code alone doesn't identify the exact failed part. 3) Get 2-3 repair estimates to compare."

What P0304 Means on Your KIA OPTIMA

P0304 is a diagnostic trouble code indicating: Cylinder 4 Misfire Detected. This code relates to the ignition system system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

4 KIA OPTIMA owners have reported this issue to NHTSA across model years 2013-2020. Most reports come from the 2013, 2016 model years. The most commonly reported component is Engine (50.0% of reports).

Real KIA OPTIMA Owner Reports

Source: NHTSA Complaints Database

"On Sunday, September 21st, 2025, my 2013 Kia Optima EX suffered sudden catastrophic engine failure while driving on the highway. The check engine light was flashing, the car misfired badly, lost complete power, and became unsafe to operate. The vehicle was then towed to Wagner Kia of Shrewsbury, MA."

— 2013 KIA OPTIMA owner · ENGINE,FUEL/PROPULSION SYSTEM · Filed 09/21/2025

"My 2016 Kia Optima is experiencing severe internal engine oil consumption that matches known issues Kia has recalled and extended warranties for. The vehicle loses 1–3 quarts of oil every few days with no external leaks."

— 2016 KIA OPTIMA owner · ENGINE · Filed 01/01/2025

"Excessive oil consumption started at 61,000 miles, causing engine misfires and dangerous power loss on the road. Engine codes 1326 and P0304 were frequent. Despite numerous services, including sensor replacements, spark plugs and oil top-offs, the problem worsened."

— 2017 KIA OPTIMA owner · POWER TRAIN,UNKNOWN OR OTHER,ENGINE · Filed 06/04/2022

"The contact owns a 2020 Kia Optima. The contact stated that while her husband was driving at an undisclosed speed, the vehicle was shuddering. The contact's husband was able to drive to the residence."

— 2020 KIA OPTIMA owner · ENGINE · Filed 09/25/2023

All reports filed by vehicle owners directly with the U.S. Department of Transportation.

📊 Complaint Trend by Model Year

1

'13

1

'16

1

'17

1

'20

Common Causes on KIA OPTIMA

Based on NHTSA complaint component analysis for this vehicle.

ENGINE 50%

ENGINE,FUEL/PROPULSION SYSTEM 25%

POWER TRAIN,UNKNOWN or OTHER,ENGINE 25%

What To Do Next

1
Check for recalls on YOUR VIN
Go to nhtsa.gov/recalls and enter your VIN. If your vehicle is covered, repairs are free.
2
Get a proper diagnosis
A code alone doesn't tell you the exact failed part. A diagnostic at a shop ($50–$150) pinpoints the root cause before you spend money on parts.
3
Compare repair quotes
Get 2–3 quotes. Dealer vs. independent shop prices often differ 30–50% for the same repair.

Frequently Asked Questions

What does P0304 mean on a KIA OPTIMA? ▾

P0304 indicates: Cylinder 4 Misfire Detected. This is a ignition system code. 4 KIA OPTIMA owners have reported this to NHTSA.

What are the most common causes of P0304 on KIA OPTIMA? ▾

Based on 4 NHTSA reports, the most commonly cited components are: Engine, Engine,Fuel/Propulsion System, Power Train,Unknown Or Other,Engine. These percentages are based on the component field in owner complaints.

Is P0304 serious on my KIA OPTIMA? ▾

Of 4 NHTSA reports for this code on KIA OPTIMA, none involved a crash or fire. However, any diagnostic code should be evaluated by a qualified mechanic.

What should I do if my KIA OPTIMA shows P0304? ▾

1) Check for recalls on your VIN at nhtsa.gov/recalls. 2) Get a professional diagnosis — a code alone doesn't identify the exact failed part. 3) Get 2-3 repair estimates to compare.