P0304
Cylinder 4 Misfire Detected
Quick answer: P0304 means cylinder 4 Misfire Detected. Fixing the underlying cause typically runs $195 to $1,150 at an independent shop. Get it checked promptly.
- Severity
- High
- Safe to drive?
- Get it checked promptly
- Typical repair
- $195 to $1,150
- Most likely cause
- A failed ignition coil on cylinder 4 (the most common cause on modern engines)
What P0304 means
The engine computer isolated the misfire to cylinder 4, so the suspects are the parts dedicated to that cylinder: its ignition coil, spark plug, and fuel injector. Cylinder-specific codes are far easier to run down than a random misfire, because swapping parts between cylinders quickly shows whether the fault travels with the part. On many four-cylinder engines cylinder 4 sits at the end of the head, where coil connectors and wiring see plenty of heat, so the wiring deserves a look too.
Common symptoms
What drivers usually notice with this code.
- Rhythmic rough idle, like the engine is limping on three cylinders
- Check-engine light flashing under hard acceleration
- Noticeable power loss and hesitation under load
- Fuel smell from the exhaust and worse fuel economy
- Occasional hard starting or extended cranking
Common causes
Ranked from most to least likely.
- 1A failed ignition coil on cylinder 4 (the most common cause on modern engines)
- 2A worn, fouled, or oil-soaked spark plug in cylinder 4
- 3A clogged or failed fuel injector on cylinder 4
- 4Chafed wiring or a heat-hardened connector at the cylinder 4 coil
- 5A vacuum leak at the cylinder 4 intake runner or gasket
- 6Low compression in cylinder 4 from valve or ring wear (the expensive end, worth confirming with a test)
Can I keep driving?
Steady light: drive gently straight to a shop. Flashing light: unburned fuel is destroying the catalytic converter as you drive, so stop and have it towed instead.
Severity: High. A flashing check-engine light always means stop, whatever the code says.
Ballpark cost
What P0304 usually costs to fix
A range, not a quote. What you pay depends on your vehicle, your area, and which of the causes above turns out to be the real one.
Typical parts and labor at an independent shop. Dealer rates run higher.
That spread is wide on purpose. P0304 points at a system, not a single part, so the real answer depends on what the diagnosis finds. Use the range to know what to expect. If an estimate comes in higher, it usually means the specific repair is more involved, and it is always fair to ask what is included.
Next steps
What to do next
Have the shop swap cylinder 4's coil and plug to a neighboring cylinder and clear the code. A misfire that follows the parts is a cheap ignition fix; one that stays on cylinder 4 points at the injector or the cylinder itself, and a compression test settles it. If a valve-cover gasket has been weeping oil into the plug wells, fix that at the same time, because oil-soaked coils are a common reason this code comes back.
Walk in informed
Ask for the diagnosis in writing and which test confirmed it, so you understand exactly what is being fixed. Fixxr shows you what the job typically costs near you, so you can approve the work with confidence.
Sources & further reading
- NHTSA — Check for vehicle safety recalls — look up open recalls for your vehicle by VIN, free
- FTC — Auto repair basics — your consumer rights at the repair shop
- AAA — Car repair and maintenance costs — independent guidance on what repairs should cost
Cost ranges and guidance reviewed July 2026.
P0304 FAQ
P0304 questions, answered
Can I drive with a P0304 code?
Steady light: drive gently straight to a shop. Flashing light: unburned fuel is destroying the catalytic converter as you drive, so stop and have it towed instead.What does the P0304 code mean?
The engine computer isolated the misfire to cylinder 4, so the suspects are the parts dedicated to that cylinder: its ignition coil, spark plug, and fuel injector. Cylinder-specific codes are far easier to run down than a random misfire, because swapping parts between cylinders quickly shows whether the fault travels with the part. On many four-cylinder engines cylinder 4 sits at the end of the head, where coil connectors and wiring see plenty of heat, so the wiring deserves a look too.What are the most common causes of a P0304 code?
The most likely causes, roughly in order, are a failed ignition coil on cylinder 4 (the most common cause on modern engines); a worn, fouled, or oil-soaked spark plug in cylinder 4; a clogged or failed fuel injector on cylinder 4; chafed wiring or a heat-hardened connector at the cylinder 4 coil. Have the shop swap cylinder 4's coil and plug to a neighboring cylinder and clear the code. A misfire that follows the parts is a cheap ignition fix; one that stays on cylinder 4 points at the injector or the cylinder itself, and a compression test settles it. If a valve-cover gasket has been weeping oil into the plug wells, fix that at the same time, because oil-soaked coils are a common reason this code comes back.How much does it cost to fix a P0304 code?
Fixing the underlying problem behind a P0304 code typically runs $195 to $1,150 at an independent shop, including parts and labor. The exact figure depends on your vehicle and which part turns out to be at fault.
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