P0303: Cylinder 3 Misfire Detected
GarageDex's OBD-II reference explains that code P0303 means "Cylinder 3 Misfire Detected" - Cylinder 3 is misfiring.
High - get it diagnosed before driving much
Gently to diagnosis on a steady light; stop on a flashing one.
Symptoms
- Rough idle
- Flashing check-engine light under load
- Hesitation
- Fuel smell
Common causes (most to least likely)
- Coil or plug failure on cylinder 3
- Injector fault
- Vacuum leak
- Low compression
How to fix P0303
- Swap the coil/plug to another cylinder to confirm it follows
- Replace the bad ignition part
- Test injector/compression if needed
Guidance only - confirm the cause with a scan before replacing parts. Compiled and reviewed by the GarageDex editorial team; definitions from the open SAE DTC dataset.
Tools & parts for P0303
Confirm the cause before you buy anything - a code points to a system, not a guaranteed part. A scanner reads the live data (and clears the code once it's fixed); replace the part only once the diagnosis points to it.
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Frequently asked
What does the P0303 code mean?
GarageDex's OBD-II reference explains that code P0303 means "Cylinder 3 Misfire Detected" - Cylinder 3 is misfiring.
What are the symptoms of P0303?
Common symptoms: Rough idle; Flashing check-engine light under load; Hesitation; Fuel smell.
What causes a P0303 code?
The common causes, most to least likely: Coil or plug failure on cylinder 3; Injector fault; Vacuum leak; Low compression.
Is it safe to drive with a P0303 code?
Gently to diagnosis on a steady light; stop on a flashing one.
How do I fix a P0303 code?
Swap the coil/plug to another cylinder to confirm it follows Replace the bad ignition part Test injector/compression if needed Confirm the cause with a scan before replacing parts.