P0304: Cylinder 4 Misfire Detected
Key takeaways
- P0304 means the engine computer detected cylinder 4 misfiring: the fuel in that cylinder isn't burning properly on some cycles.
- Keep driving to short, gentle trips; if the check engine light flashes, pull over and stop, because unburned fuel can overheat the catalytic converter.
- Swapping the cylinder 4 ignition coil with a neighbor and seeing if the misfire moves is the cheapest first test.
- Most P0304 fixes are a spark plug ($150–$350 for a 4-cylinder set) or an ignition coil ($120–$300); low compression is the rare expensive case at $1,500–$4,500.
- Ford has several bulletins for misfires on 2023–2025 EcoBoost engines, and many makes have engine-computer software updates that name P0304.
What P0304 means
Cylinder 4 isn’t firing properly: on some cycles, the fuel in that cylinder isn’t burning. The scanner name is Cylinder 4 Misfire Detected. The engine computer watches the crankshaft speed through the crankshaft position sensor. Every time a cylinder fires, the crank speeds up a little. When cylinder 4’s power stroke doesn’t give that push, the computer counts a misfire. Once the count passes its limit over a set number of revolutions, P0304 sets. A misfire needs one of three things to go wrong in that cylinder: spark, fuel, or compression.
Is it safe to drive?
Short trips, gently, while the light is steady. A misfiring cylinder sends raw fuel into the exhaust, and the catalytic converter can overheat trying to burn it. That’s how a $150 coil job becomes a $1,500+ converter job. If the check engine light flashes, the misfire is bad enough to damage the converter right now: pull over when it’s safe and stop driving. The same goes for heavy shaking, a smell of fuel, or loss of power on the highway. Our check engine light flashing guide explains why.
Causes, ranked
| Cause | How you confirm it | Typical cost (US independent shop, 2026) |
|---|---|---|
| Worn or fouled spark plug | Plug gap worn wide, tip oily or black, cracked insulator; plugs past their service interval | $150–$350 a set (4-cyl), $250–$600 (V6/V8) |
| Failing ignition coil | Swap coil 4 with a neighbor; the code moves (e.g. to P0303) | $120–$300 per coil |
| Wiring or connector at coil 4 or injector 4 | Loose, corroded or oil-soaked plug; code comes and goes over bumps | $0–$250 |
| Clogged or failed fuel injector | Swap injectors or test balance; injector doesn’t click | $100–$200 cleaning; $250–$600 per injector |
| Vacuum leak near cylinder 4 | Hissing at idle, cracked hose or intake gasket; lean fuel trims | $50–$400 |
| Low compression (burnt valve, head gasket, worn rings) | Compression or leak-down test shows cylinder 4 well below the others | $1,500–$4,500 |
What to check first
- Note when it happens. Cold start, idle, under load, in the rain? It tells the shop where to look. Our rough idle article covers idle-only misfires.
- Check the plug service history. If the plugs are near or past their interval, replacing all of them is often the first real repair.
- Swap the coil. On coil-on-plug engines, move coil 4 to another cylinder, clear the code, and drive. If the misfire moves with it, you’ve found it. If it stays on cylinder 4, look at the plug, the injector, and then compression.
- Look at the connectors. Oil in the spark plug well from a leaking valve cover gasket can short the coil. Fix the leak or the new coil will fail too.
- Compression test before big money. If spark and fuel check out, a compression or leak-down test settles whether it’s mechanical.
- Check bulletins. Among the bulletins naming P0304, Ford has several for misfires on 2023–2025 EcoBoost engines (Escape, Corsair, Nautilus, Mustang, Explorer) and a 2024 F-150 PowerBoost software update. Jeep, Ram and Acura also have engine-computer updates listing it. On those models, ask a dealer before buying parts.
What it costs
The cheap outcome is one coil or a set of plugs, $120–$350. The common outcome is plugs plus a coil, or an injector, a few hundred dollars. The expensive outcome is a compression problem, $1,500–$4,500, which is rare but real. Diagnosing first matters here: a coil swap is free and tells you more than guessing, and a compression test before a big repair keeps you from replacing coils on an engine with a burnt valve.
Related codes
P0304 often appears with P0300 (random misfire), and with neighbors like P0302 when a shared part is failing. If several cylinders misfire at once, look at things they share: fuel pressure, a vacuum leak, or bad gas. If the car shakes along with the light, see check engine light and car shaking or ask our AI mechanic.
What owners report to NHTSA
356 complaints filed with NHTSA mention P0304, 328 of them since 2015, across 95 different models. The component owners most often filed it under: engine.
Most-reported models
| Vehicle | Complaints | Model years reported |
|---|---|---|
| FORD ESCAPE | 50 | 2013, 2016, 2017, 2018, 2019 |
| FORD EDGE | 29 | 2015, 2016, 2017, 2018 |
| HONDA ODYSSEY | 20 | 2012, 2013, 2014, 2015, 2016 |
| HONDA CR-V | 20 | 2000, 2017, 2018, 2019 |
| HONDA ACCORD | 20 | 2011, 2016, 2018, 2019, 2022 |
| FORD FUSION | 18 | 2013, 2015, 2016, 2017, 2019 |
| HONDA PILOT | 12 | 2011, 2012, 2013, 2015, 2016 |
| CHEVROLET SILVERADO 1500 | 9 | 2008, 2017, 2020, 2021, 2023 |
| KIA SORENTO | 9 | 2013, 2014, 2016, 2020, 2022 |
| HONDA FIT | 8 | 2018, 2019 |
Manufacturer service bulletins that name P0304
485 technical service bulletins and manufacturer communications filed with NHTSA mention P0304, from 30 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:
- ACURA ACURA (2021, 2022, 2023, 2019), bulletin 10233209: Service Bulletin - Under certain circumstances, the vehicle may experience driveability concerns. This may result in the following DTCs to set: P0300 (Random Misfire Detected), P0301 (No. 1 Cylinder Misfire Detected), P0…
- RAM 1500 (2025), bulletin 11008018: "Flash: Powertrain Control Module (PCM) Updates Customers must experience a Malfunction Indicator Lamp (MIL) illumination and the vehicle must exhibit/set one or more of the following Diagnostic Trouble Codes (DTCs): P01…
- LINCOLN NAUTILUS (2024, 2025, 2023), bulletin 11010920: Some 2023-2025 Escape/Corsair vehicles equipped with a 1.5L or 2.0L EcoBoost engine, 2024 Mustang vehicles equipped with a 2.3L EcoBoost engine, 2024-2025 Nautilus, and 2025 Explorer vehicles equipped with a 2.3L EcoBoos…
- FORD EXPLORER (2025, 2023, 2024), bulletin 11010920: Some 2023-2025 Escape/Corsair vehicles equipped with a 1.5L or 2.0L EcoBoost engine, 2024 Mustang vehicles equipped with a 2.3L EcoBoost engine, 2024-2025 Nautilus, and 2025 Explorer vehicles equipped with a 2.3L EcoBoos…
- FORD MUSTANG (2024, 2023), bulletin 10253555: Some 2023-2024 Escape/Corsair vehicles equipped with a 1.5L or 2.0L EcoBoost engine, 2024 Mustang vehicles equipped with a 2.3L EcoBoost engine, and 2024 Nautilus vehicles may exhibit an engine misfire condition with dia…
- LINCOLN CORSAIR (2023, 2024), bulletin 10253555: Some 2023-2024 Escape/Corsair vehicles equipped with a 1.5L or 2.0L EcoBoost engine, 2024 Mustang vehicles equipped with a 2.3L EcoBoost engine, and 2024 Nautilus vehicles may exhibit an engine misfire condition with dia…
Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.
Frequently asked questions
Can I drive with a P0304 code?
Short, gentle trips only, and only while the light is steady. If the light flashes or the engine shakes hard, stop. A misfiring cylinder sends unburned fuel into the exhaust, which can overheat and ruin the catalytic converter.
What is the most common cause of P0304?
A worn spark plug or a failing ignition coil on cylinder 4. Swapping the coil to another cylinder and seeing if the code follows it (to P0303, say) confirms which one.
How much does it cost to fix P0304?
Usually $150–$350 for spark plugs on a 4-cylinder or $120–$300 for one ignition coil at an independent shop. An injector runs $250–$600. Low compression from a valve or head gasket problem is the rare $1,500–$4,500 case.
Which cylinder is number 4?
It depends on the engine. On most inline 4-cylinders it's the one at the end opposite the timing belt or chain. On V6 and V8 engines the numbering differs by maker, so check a service manual or ask a shop before swapping parts.
Can a P0304 fix itself?
The light can go off if the misfire stops, but the cause is usually still there. Worn plugs and weak coils get worse, especially under load and in damp weather.
References
- NHTSA ODI complaints flat file (FLAT_CMPL)
- NHTSA manufacturer communications / technical service bulletins flat files
- 40 CFR 86.1806-17: Onboard diagnostics (EPA OBD requirements, incl. misfire monitoring)
- 13 CCR 1968.2: Malfunction and diagnostic system requirements (California OBD II, misfire monitoring and MIL blinking)