Ignition and misfires code
P0303: Cylinder 3 misfire
How this range is built
| Part of the job | Low | High |
|---|---|---|
| Parts | $30 | $120 |
| Labor: 0.4 to 1.2 hours × $125 to $175 an hour | $50 | $210 |
| Fees: shop supplies, disposal, diagnostics | $0 | $15 |
| Total, rounded | $80 | $350 |
The hourly rate is the BLS Occupational Employment and Wage Statistics, May 2025 average pay for this trade in Boston, $31.54 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.
The engine computer tracks the crankshaft's speed after each cylinder fires, and cylinder 3 is falling behind. That tells it cylinder 3 is missing some of its burns. It stays on a steady light unless the misses get heavy enough to flash.
- Safe to drive?
- Short trips only
- Most common cause
- Worn spark plug in cylinder 3
A steady light means short drives are okay; a flashing light means stop, because raw fuel can ruin the catalytic converter.
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 3
- Failing ignition coil on cylinder 3
- 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 for the cylinder 3 coil to be swapped with cylinder 2 or 4 and the code cleared. If the code follows the coil to the new number, replace that coil. If not, the plug, injector or a leak near cylinder 3 comes next.
Other repairs that sometimes fix P0303
| Repair | Typical range, Boston |
|---|---|
| Spark plug replacement | $95 to $580 |
| Fuel injector replacement (one injector) | $180 to $910 |
| Vacuum leak repair | $100 to $530 |
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. Massachusetts rules 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).
P0303 questions
How do I know which cylinder is number 3?
The numbering depends on your engine layout. On many inline engines it is the third from the front, but on V engines it follows the firing banks. A repair diagram for your exact engine settles it fast.
Should I replace the plug or the coil?
Replace the plug if it is old, since it is inexpensive and a regular cause. If the coil swap moves the miss, replace the coil. Doing the test first saves you from paying for both when only one is bad.
Can I keep driving with this code?
A short, easy drive is usually fine with a steady light. Do not tow, climb hard or push the engine, and if the light begins to flash, stop soon because the converter can overheat from raw fuel.
How much does it cost to fix P0303?
The most common fix, ignition coil replacement (one coil), has a typical range of $80 to $350 in Boston. It is an estimate built from parts prices and local labor wages, not a quote. Your car and shop change it.
P0303 repair cost by city
Related codes
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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.