P0306 — Cylinder 5 Misfire Detected
Drivable short-term, but fix now to avoid damage.
What P0306 means
This code means the engine computer detected a misfire on cylinder 5, where the air-fuel mixture isn't igniting correctly. The usual culprits are a worn spark plug, a failing ignition coil, or a fuel injector issue, though vacuum leaks and low compression are also possible. Typical fixes involve replacing the spark plug or coil for cylinder 5, and most cases are repairable without tearing into the engine.
Common symptoms
- Check engine light is on or flashing
- Rough idle or engine shaking
- Loss of power or sluggish acceleration
- Hesitation or stumbling under load
- Increased fuel consumption
Common causes
- Worn or fouled spark plug on cylinder 5
- Failing ignition coil for cylinder 5
- Clogged or faulty fuel injector
- Vacuum leak near cylinder 5
- Low compression from worn valves or rings
Typical repair cost
$100 – $500
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0306 code?
Only briefly and gently. A misfiring cylinder 5 sends unburned fuel into the exhaust and can damage your catalytic converter fast. If the light is flashing, stop and tow it; if steady, drive carefully straight to a mechanic.
How much does it cost to fix a P0306 code?
Typically $100 to $500. A spark plug or single coil is inexpensive, while injector or compression repairs cost more. A proper diagnosis first avoids guessing and replacing parts unnecessarily.
Is a P0306 code serious?
Yes. Misfires are serious because they can ruin the catalytic converter and leave you with a much bigger bill. The upside is that the root cause is often a cheap, common part like a plug or coil.
Could a P0306 be caused by something other than the spark plug?
Definitely. While plugs and coils are the most common causes, a clogged injector, a vacuum leak, or low compression on cylinder 5 can also trigger it. That's why a scan and a few quick tests are worth doing before buying parts.