P0303 on KIA OPTIMA — Cylinder 3 Misfire Detected

Q: "What does P0303 mean on a KIA OPTIMA?"

"P0303 indicates: Cylinder 3 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 P0303 on KIA OPTIMA?"

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

Q: "Is P0303 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 P0303?"

"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 P0303 Means on Your KIA OPTIMA

P0303 is a diagnostic trouble code indicating: Cylinder 3 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 2012-2017. Most reports come from the 2017, 2012 model years.

Real KIA OPTIMA Owner Reports

Source: NHTSA Complaints Database

"The contact owns a 2012 Kia Optima. The contact stated while driving approximately 70 MPH, the check engine warning illuminated, and the vehicle lost motive power. The contact stated that the engine was running however, the vehicle failed to respond as needed."

— 2012 KIA OPTIMA owner · ENGINE AND ENGINE COOLING · Filed 11/27/2022

"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

"Engine is failing and using over 3 quarts of oil every 700-100 miles. Spark Plugs have become oil fouled and replaced all 4 spark plugs June 11th, 2024 and replaced all 4 spark plugs again January 12th, 2025."

— 2017 KIA OPTIMA owner · POWER TRAIN,ENGINE · Filed 07/07/2025

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

📊 Complaint Trend by Model Year

1

'12

1

'13

2

'17

Common Causes on KIA OPTIMA

Based on NHTSA complaint component analysis for this vehicle.

ENGINE and ENGINE COOLING 25%

ENGINE,FUEL/PROPULSION SYSTEM 25%

POWER TRAIN,ENGINE 25%

POWER TRAIN 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 P0303 mean on a KIA OPTIMA? ▾

P0303 indicates: Cylinder 3 Misfire Detected. This is a ignition system code. 4 KIA OPTIMA owners have reported this to NHTSA.

What are the most common causes of P0303 on KIA OPTIMA? ▾

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

Is P0303 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 P0303? ▾

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.