P0303 Cylinder 3 Misfire
Caution
Cylinder 3 is misfiring. Check its spark plug and swap its coil before you buy anything. Fix it within days; if the light flashes, slow down and stop soon.
- Safe to drive?
- Only gently, and not if the light flashes
- Typical cost at a shop
- $216-$953 RepairPal national averages, parts and labor
- Emissions test
- Yes, while the check engine light is on, most OBD emissions tests fail the car.
- Carmaker bulletins
- 2 notes with links
What it means
The crankshaft slows each time cylinder 3 should fire but does not. As with any single-cylinder misfire, the cause is one of the few things that serve that cylinder: its spark, its fuel, its air seal or its compression.
The technical version
Same monitor as P0300 and P0301, attributed to cylinder 3. Where the car supports Mode 06, the cylinder 3 misfire counts show how often it misses on each drive.
Official name: Cylinder 3 Misfire Detected.
Symptoms
- A shake at idle.
- A stumble under load.
- A flashing light if it is bad.
Causes, most likely first
| Cause | How likely | How to tell |
|---|---|---|
| A worn or fouled spark plug in cylinder 3 | most common | Plug past its interval. |
| Cylinder 3's ignition coil | common | The misfire follows the coil when you swap it. |
| A clogged or dead injector on cylinder 3 | less common | The misfire follows the injector. |
| A vacuum leak at cylinder 3's intake runner | less common | Misfire mostly at idle. |
| Low compression in cylinder 3 | rare | A compression test shows it. |
How likely is our ranking from repair data and common practice, not a published rate.
What the live data shows
Cylinder 3's misfire count rising alone is the confirmation, where the car reports it. Counts during acceleration point to the coil or plug; counts at warm idle point to the injector or a runner leak. The freeze frame records the conditions when it set.
What to check first, in order
-
If the light flashes, slow down and stop soon.
Protects the converter.
What the data shows: Counts rise fast.
Cost: free
-
Replace or inspect the cylinder 3 spark plug.
Most common cause.
What the data shows: Counts drop after the change.
Cost: $288-$399 at a shop (Spark plug replacement, RepairPal)
-
Swap coil 3 with a neighbor.
Free coil test.
What the data shows: If the code moves to the other cylinder, replace the coil.
Cost: $238-$320 at a shop (Ignition coil replacement, RepairPal)
-
Swap-test or clean the injector.
Next most likely.
What the data shows: Counts follow the injector.
Cost: $768-$953 at a shop (Fuel injector replacement, RepairPal)
-
Compression-test cylinder 3.
Last step.
What the data shows: Not a scanner step.
Cost: a shop test
Is it safe to drive?
Caution
Only gently, and not if the light flashes. Unburned fuel reaches the converter.
Steady light with a light stumble: drive gently and get it fixed within days. Flashing light: raw fuel is overheating the catalytic converter; slow down and stop as soon as it is safe. A misfire left alone tends to turn into a P0420.
Stop driving and get help if
- The check engine light flashes.
- The engine shakes hard.
What it costs
| Repair | Typical cost |
|---|---|
| Engine compression testRepairPal, updated September 3, 2026 | $216-$317 |
| Ignition coil replacementRepairPal, updated September 3, 2026 | $238-$320 |
| Spark plug replacementRepairPal, updated September 3, 2026 | $288-$399 |
| Fuel injector replacementRepairPal, updated September 3, 2026 | $768-$953 |
National averages for the full job at a shop, parts and labor, from RepairPal (updated September 3, 2026). Your price depends on the car and the area. Many of the first checks on this page cost nothing with a scanner. Ignition coil and spark plugs together were CarMD's number 3 check engine repair in 2025 ($480), ignition coil alone number 5 ($256), spark plugs alone number 10 ($299). Fuel injectors were number 7, at an average of $572. CarMD averages come from a different method (repairs reported by its users), so they can sit below RepairPal's shop estimates.
Sources for the notes: CarMD 2026 Vehicle Health Index (press release, April 22, 2026).
Can I clear it? Will it come back?
After the repair, clear the code and check cylinder 3's count after the next drive.
Will it fail an emissions test?
Yes, while the check engine light is on, most OBD emissions tests fail the car.
Carmaker notes
Service bulletins and warranty extensions that name this code. Ask a dealer to check your VIN.
-
Honda 2008-2012 Accord V6 automatic
Honda bulletin 13-078 (version 11, December 2018): piston rings on some cylinders can line up and foul the spark plugs, with P0301 to P0304. Coverage is 8 years from purchase with unlimited miles, from a class action settlement.
Honda 13-078 via NHTSA static.nhtsa.gov
-
Ford 2014-2019 Fusion and 2017-2019 Escape 1.5L EcoBoost
Ford bulletin 19-2139 (November 2019): P0300 to P0304 and related codes may come from coolant getting into a cylinder. The fix is a new short block and head gasket.
Ford TSB 19-2139 via NHTSA static.nhtsa.gov
Related codes
Also related, no guide yet: P0302, P0304.
How Obie handles P0303
Obie reads the cylinder 3 misfire count where your car reports it, guides the coil swap, and checks again after the next drive. Obie is part of ScanMyCar Pro. Codes and live sensors are free.
Questions people ask
What causes a cylinder 3 misfire?
Most often the spark plug or the coil on that cylinder, then the injector.
Can I drive with P0303?
Gently, for a few days, with a steady light. Not with a flashing light.
How do I test the coil?
Swap it with another cylinder's coil and drive. If the misfire moves, the coil is bad.
Sources
- RepairPal: P0303 code page repairpal.com
- RepairPal: Engine compression test (updated September 3, 2026) repairpal.com
- RepairPal: Ignition coil replacement (updated September 3, 2026) repairpal.com
- RepairPal: Spark plug replacement (updated September 3, 2026) repairpal.com
- RepairPal: Fuel injector replacement (updated September 3, 2026) repairpal.com
- CarMD 2026 Vehicle Health Index (press release, April 22, 2026) prnewswire.com
- Honda 13-078 via NHTSA static.nhtsa.gov
- Ford TSB 19-2139 via NHTSA static.nhtsa.gov
- Texas DPS emissions testing FAQ dps.texas.gov
- Arizona myazcar.com: OBD and the check engine light myazcar.com
A guide, not a diagnosis. This page describes what P0303 generally means across OBD2 cars. What is actually wrong with your car depends on its live data and its history, and any repair decision deserves a proper diagnosis, whether that is you with a scanner or a professional with a lift.
