P0304: Cylinder 4 Misfire Detected
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Short careful trips only while the light stays steady. If it starts FLASHING, stop as soon as it is safe - that is the computer reporting active catalyst-damaging misfire, not a suggestion.
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
“Cylinder misfire (e.g., Code P0301-P0304) Low coolant levels with no visible leaks Rough idle/shaking on startup Check engine light”2017 Ford Edge · Sep 2026
“I will be accelerating and the car will on occasion start to sputter like it is going to die and loose power on me. It has done it three different times the last time it through a code on my OBD monitor read it and said P0304 the 4th cylinder is misfiring. I took it in and they couldn't see the code or even the history of there being a code thrown. Please help my ladst car that did this needed to have the engine replaced and is recall was issued after we sold it to a junk yard, and I can't afford that again.”2023 Kia Soul · Sep 2026
“Vehicle has roughly 64,000 miles on it. As we were actively driving, vehicle suddenly lost power and completely shut off. This was a sudden stall. Vehicle would not crank back up but starter would engage. Upon scanning the trouble codes, multiple codes came up in regard to the fuel pump issue that is currently under investigation. (P008A, P00C6, P0304) This issue poses a serious risk as while actively driving, could cause an accident and should be an active recall for this year make and model.”2022 Ford Expedition · Sep 2026
Show 7 more owner reports
“- Vehicle experienced a cylinder-specific misfire (P0304) at ~60,000 miles - Dealer diagnosed a faulty fuel injector, confirmed as a known issue covered by Honda Service Bulletin 22-002 - The misfire caused rough running / hesitation - As part of the service bulletin, Honda offered to replace the fuel injectors under the following conditions: <10 years from purchase date, <150,000 miles”2016 Honda Fit · Sep 2026
“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
“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
Cars that report P0304 most often
Based on mentions of this code in NHTSA owner complaints.
P0304 by make
Makes with enough NHTSA reports of P0304 for a page of their own - which models and years report it.
Frequently asked questions
Can I drive with P0304?
Short careful trips only while the light stays steady. If it starts FLASHING, stop as soon as it is safe - that is the computer reporting active catalyst-damaging misfire, not a suggestion.
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.