Diagnostic code
P0303 Code: Cylinder 3 Misfire Detected
P0303 means cylinder 3 has a repeat misfire pattern. A technician will usually confirm the cylinder location, inspect ignition parts, check injector behavior, and rule out compression or valve problems before replacing parts.
Can I drive?
Stop driving if the light flashes, the engine shakes strongly, or exhaust smells raw. Otherwise keep driving limited until repair.
Repair range
$100-$1,400
Scanner note
Basic OBD-II scanner with live data
Plain-English Meaning
P0303 means cylinder 3 has a repeat misfire pattern. A technician will usually confirm the cylinder location, inspect ignition parts, check injector behavior, and rule out compression or valve problems before replacing parts.
Common Causes
Symptoms
- Shaky idle
- Hesitation
- Poor fuel economy
- Check engine light after acceleration
Diagnostic Steps
- 1Find cylinder 3 on the specific engine
- 2Inspect the plug and coil connection
- 3Swap coil or injector if safe to test
- 4Check fuel trim and misfire counters
- 5Perform compression or leak-down testing when needed
Confusable And Related Codes
P0300
Compare →P0300 means the engine is misfiring randomly or across multiple cylinders instead of one clearly identified cylinder. Ignition, fuel, air leaks, compression problems, or timing issues can all interrupt combustion and trigger this code.
P0301
Compare →P0301 means cylinder 1 is not burning its air-fuel mixture consistently. The problem may be isolated to that cylinder, such as a spark plug, coil, injector, compression issue, or local air leak near the intake runner.
P0302
Compare →P0302 means cylinder 2 is misfiring enough for the engine computer to identify it. The cause may be electrical, fuel-related, mechanical, or an air leak that affects that cylinder more than the others.
P0304
Compare →P0304 means cylinder 4 is not firing reliably. The code narrows the search to one cylinder, but the final cause still has to be separated between spark, fuel, air, compression, and wiring faults.
FAQ
Is P0303 serious?
Yes when symptoms are strong or the light flashes, because converter damage can happen quickly.
Can P0303 be an injector?
Yes. An injector that is clogged, leaking, or not commanded correctly can misfire one cylinder.
Why does P0303 happen under load?
Ignition weakness often shows up under load because the spark has to work harder.
This page is educational and is not a substitute for hands-on vehicle diagnosis. Source notes: Code meaning verified against OBD-II reference sources; explanation is original.