Ignition and misfires code
P0304: Cylinder 4 misfire
How much to fix P0304? Typically $70–$320.
Wide range: this job varies a lot. Itemize your quote for a better answer.
How this range is built
| Part of the job | Low | High |
|---|---|---|
| Parts | $30 | $120 |
| Labor: 0.4 to 1.2 hours × $110 to $150 an hour | $44 | $180 |
| Fees: shop supplies, disposal, diagnostics | $0 | $15 |
| Total, rounded | $70 | $320 |
The hourly rate is the BLS Occupational Employment and Wage Statistics, May 2025 average pay for this trade in the US, $27.13 an hour, times 4 to 5.5 to cover what a shop bills (overhead, tools, insurance, profit). Parts are a band from budget aftermarket to the manufacturer part. Full method.
Not a repair shop, estimates only. Typical range, estimate. Not a quote. Your car, parts and shop change the number.
This is the range for the most common fix, ignition coil replacement (one coil). Which repair your car needs depends on a proper diagnosis.
Cylinder 4 is not completing its burn every time. The computer picked this out by watching tiny dips in the crankshaft's rotation that line up with cylinder 4's turn to fire. The engine still runs, but it shakes more than it should.
- Safe to drive?
- Short trips only
- Most common cause
- Worn spark plug in cylinder 4
A steady light means short drives are okay; a flashing light means stop, because raw fuel can ruin the catalytic converter.
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What you may notice
- Shaking, worse at idle
- Flashing check-engine light
- Hesitation when accelerating
- Often a stronger fuel smell
Common causes, most likely first
- Worn spark plug in cylinder 4
- Failing ignition coil on cylinder 4
- Clogged or weak fuel injector for that cylinder
- Vacuum leak near that cylinder
- Low compression from a valve or ring problem
Check this first
Ask the shop to move the cylinder 4 coil to cylinder 3 and see where the code goes. If it follows, the coil is bad. If it stays, a worn plug, weak injector or a small intake leak near cylinder 4 is next on the list.
Other repairs that sometimes fix P0304
| Repair | Typical range, US |
|---|---|
| Spark plug replacement | $85 to $510 |
| Fuel injector replacement (one injector) | $170 to $820 |
| Vacuum leak repair | $90 to $460 |
Before you pay
- Ask the shop what test showed this part is the cause, not just that the code appeared.
- Ask for parts and labor listed separately, and for the hours.
- Ask for a written OK before any extra work. Many states require written authorization before repairs.
Got a quote already? Check it against the range. Want to see if your car has a recall tied to this problem? Check recalls by VIN.
Need to read a code yourself? OBD-II scanners on eBay (affiliate link, disclosure).
P0304 questions
How do I know which cylinder is number 4?
On a four-cylinder engine it is usually the last one, near the transmission or the far end from the belts. On a V6 or V8 the numbering follows the bank layout, so check your engine's diagram.
Should I replace the plug or the coil?
Start with the plug if it is overdue, and use a coil swap to see whether the coil is at fault. This way you replace only the part that failed instead of the whole ignition set.
Can I keep driving with this code?
Short, gentle trips are usually okay while the light is steady. Avoid towing or hard acceleration, and pull over if the light flashes, since a strong misfire can overheat the catalytic converter in minutes.
How much does it cost to fix P0304?
The most common fix, ignition coil replacement (one coil), has a typical range of $70 to $320 across the US. It is an estimate built from parts prices and local labor wages, not a quote. Your car and shop change it.
Typical range in 10 metro areas
Only the labor rate changes between cities. Same parts, same hours.
| Area | Typical range, estimate |
|---|---|
| Boston area, Massachusetts | $80 to $350 |
| New York City area | $75 to $340 |
| Los Angeles area, California | $75 to $340 |
| Chicago area, Illinois | $75 to $330 |
| Houston area, Texas | $70 to $310 |
| Dallas-Fort Worth area, Texas | $70 to $310 |
| Phoenix area, Arizona | $70 to $320 |
| Atlanta area, Georgia | $75 to $330 |
| Miami area, Florida | $70 to $320 |
| Seattle area, Washington | $80 to $340 |
Related codes
More ignition and misfires codes
Code meaning written in our own words. Some codes mean different things on different makes, so check your scan tool or manual. Not a repair shop, estimates only.