P0309 — Cylinder 9 Misfire Detected

What Does P0309 Mean?

P0309 is a diagnostic trouble code indicating: Cylinder 9 Misfire Detected. This code relates to the ignition system system. It has been reported in NHTSA complaints across 2 different vehicle models.

Symptoms of P0309

⚠️ Engine misfires
⚠️ Loss of engine power

Common Causes

🔍 Worn or fouled spark plugs

P0309 Reports by Year

2012

1

2023

1

Real Owner Reports

From NHTSA complaint database — actual owner descriptions.

"ON A RECENT COLD MORNING I GOT INTO MY 2009 NISSAN ALTIMA, AT 7:00 AM AND DROVE SON TO SCHOOL. CAME HOME AND PARKED VEHICLE. GOT BACK IN CAR AT 3:00 PM AND CAR WOULD NOT START. THE CAR HAD BEEN FINE THAT MORNING. PUSH START WOULD NOT GET OUT OF "LOCK" POSITION. HEADLIGHTS, INSIDE LIGHTS, BRAKE LIGH"
— Nissan Altima owner, 12/12/2012

"Loss of power. Was driving across a 4 lane intersection and the vehicle lost power. The engine light came on. I stopped and check the oil and it was 2 quarts low. We had just changed oil less than 2,000 mikes ago. I tool the car to parts store and they said it was a p0309 code. That #4 cylinder mis"
— Kia Optima owner, 12/24/2023

Source: NHTSA Complaints Database

Most Reported Vehicles for P0309

Based on NHTSA owner complaint data.

#	Vehicle	Reports
1	NISSAN ALTIMA
2	KIA OPTIMA

Frequently Asked Questions

Can I drive with a misfire code?

Driving with active misfires can damage your catalytic converter (a $1,000+ repair). Get it fixed promptly.

Should I replace all ignition coils at once?

Not necessarily. Replace the failed coil, but if your vehicle has 100K+ miles, consider replacing all coils and spark plugs as preventive maintenance.

Will this code come back after repair?

If the root cause is fixed properly, no. However, if only the symptom (e.g., spark plug) is replaced without addressing the underlying issue, it may return.

What To Do Next

Possible Fixes

🔧 Have the code scanned with a professional-grade scanner to read freeze frame data
🔧 Replace spark plugs if over 60,000 miles; inspect ignition coils
🔧 If DIY repair isn't feasible, get a diagnostic from a trusted mechanic ($50-150)

1
Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
3
Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.

P0309: Cylinder 9 Misfire Detected