P0304: Cylinder 4 Misfire Detected
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Short careful trips only - keep engine load light until repaired.
Symptoms
- Flashing check engine light under load
- Rough running, especially cold
- Fuel smell from the exhaust
Likely causes, most common first
- Spark plug or coil on cylinder 4
- Injector not delivering
- Vacuum leak at that runner
- Burnt exhaust valve
Read P0304 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0304 is the most common single-cylinder misfire simply because cylinder 4 exists on every four-cylinder engine on the road, and on many of them it sits at the end of the head where coolant flow and heat distribution are least favourable.
On a four-cylinder the diagnosis is unusually cheap: everything is accessible, and plugs and coils are normally replaced as a set anyway. If new ignition parts do not clear it, a compression and leak-down test on that cylinder is the next step - a burnt exhaust valve on the end cylinder is a recognised pattern on several high-mileage engines.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Owner reports mentioning P0304
“vehicle may experience driveability issues, which may result in DTCs P0300 (random misfire detected), P0301 (No. 1 cylinder misfire detected), P0302 (No. 2 cylinder misfire detected), P0303 (No. 3 cylinder misfire detected), P0304 (No. 4 cylinder misfire detected), or P0172 (fuel system too rich) or a whirling noise coming from the engine compartment. POSSIBLE CAUSE Based on certain driving patterns and environmental factors, the DTC's stated above may be set or a whirling noise may occur. Apparently only certain vin numbers were affected, mine is not in the list but im still having the exact same issues.”2017 Honda CR-V · Aug 2026
“Received P0304 code for 4th cylinder missfire. Appears to be affected by the know coolant intrusion issue with these models”2017 Ford Escape · Aug 2026
“receiving code p0304 cylinder 4 misfire. technician placed scope inside cylinder 4 and signs of coolant inside the cylinder. TSB 19-2346 matches what is happening in with his vehicle”2018 Ford Edge · Jul 2026
Show 7 more owner reports
“Emission warning light along with LKAS, ACC, Brake system are coming on the DASH. No driveability issues. The dealership in Walnut Creek pull code and find P0304 missfire #4 CYCLINDE, test #1 and #2 FAIL. Recommending to replace all 4 injectors.”2017 Honda CR-V · Jul 2026
“Coolant Intrusion due to a design flaw leading to coolant entering the combustion chamber causing spark plugs to prematurely fail and in extreme cases cause the engine to hydrolock and bend piston rods. Symptoms are a rough idle, MIL illumination and DTC for Misfires P0300-P0304, Coolant loss and overheating”2018 Ford Escape · Jun 2026
“The contact owns a 2018 Land Rover Discovery Sport. The contact stated that while driving at an undisclosed speed, and while the vehicle was idling, there was an abnormal rattling sound coming from the vehicle. The vehicle lost motive power and the transmission failed to shift properly. The contact conducted was able to retrieve DTC: P1315, P0304, P0316, P054A and P0014. The dealer was not notified of the failure. The manufacturer was notified of the failure. The approximate failure mileage was 72,000.”2018 Land Rover Discovery Sport · Mar 2026 · 72,000 mi
“Vehicle suffered acute catastrophic engine failure. No dash lights alerted me. Engine just started rattling and smoking. Dealership it was towed to pulled codes p0302 p0304 p0012 p0014 tried to blame it on us despite known coolant intrusion issue”2017 Ford Escape · Mar 2026
“On [XXX], check engine light came on with P1327 (PNSS piston noise detection). History includes SC209 recall in 2021 (inspection passed, PNSS software added Feb 2022). Now at 94,000 miles with misfire P0304 on cyl 4 and timing correlation P0017-dealer refuses full engine replacement under recall. Service dealer insisted it would be safe to drive 300 miles to Billings, MT from my home base location. Got 5 miles down the road to be left stranded to walk back with no service on a 13 degree day. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)”2021 Kia Seltos · Feb 2026
“The contact owns a 2020 Kia Soul. The contact stated that while driving at an undisclosed speed, the vehicle failed to accelerate as needed. Additionally, the engine was leaking oil. The check engine warning light was illuminated. The contact stated that the vehicle was previously repaired under NHTSA Campaign Number: 21V259000 (Engine); however, the failure recurred. The contact's friend diagnosed the vehicle with a code reader and retrieved DTC: P0017, P0301, P0302, P0303, and P0304. The vehicle was not diagnosed or repaired by an independent mechanic or dealer. The manufacturer was not made aware of the failure. The failure mileage was approximately 92,000.”2020 Kia Soul · Feb 2026 · 92,000 mi
“At 80000miles I noticed misfires and replaced original spark plugs per spec At 107578, misfires occurred, when I pulled plugs pos 1 was completely worn out, as well as pos 4.Codes were seen P0304 and P0301. Car ran well after replacement. I have been troubled by loss of coolant lately and could find no leaks. Also temp gauge in dash "wanders" Being retired I can't afford to go to dealership. I believe spark plugs should not wear out after approx 25000 miles No overheating of engine has occurred . I drive about 12000/yr. Car is available to be seen. Dealer has not seen car Concerned problem could cause engine failure. Thank you”2018 Ford Focus · Feb 2026
Cars that report P0304 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0304?
Short careful trips only - keep engine load light until repaired.
How much does it cost to fix P0304?
Typical US repair costs range from $20 for the simplest fix (spark plug) to $2,500 in the worst case. The right number depends on which cause your car has - see the causes list.
Related codes
The codes closest to P0304. They often appear together, and telling them apart is usually what narrows the diagnosis.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.