P0305 Code: Cylinder 5 Misfire Detected
Quick Answer
Cylinder 5 is misfiring — combustion is incomplete or absent in that cylinder.
At a Glance
What this code means
P0305 is a single-cylinder misfire code for cylinder 5. On 6-cylinder and 8-cylinder engines, cylinder 5 is often on the passenger side (Bank 2). The ECU monitors crankshaft speed variations to detect which cylinder is failing to produce a complete power stroke.
A misfire happens when combustion fails in one cycle. The crankshaft loses speed at that cylinder, which the ECU detects as a misfire event.
Common causes
- Worn or fouled spark plug in cylinder 5
- Failed ignition coil for cylinder 5
- Clogged or leaking fuel injector on cylinder 5
- Low compression in cylinder 5
- Vacuum leak at the intake manifold near cylinder 5
Symptoms you might notice
- Rough idle or vibration (especially noticeable on 6-cylinder engines)
- Steady or flashing check engine light
- Reduced power output
- Hesitation under acceleration
- Possible raw fuel smell from exhaust
Can you still drive?
Flashing check engine light — stop immediately. Steady light — avoid prolonged driving until repaired.
How serious is this code?
High if the light is flashing. Moderate with a steady light.
Before you replace parts
Parts replacement is often not the first step. Before buying anything, it's worth checking these basics:
- Perform the coil-swap test first — move the cylinder 5 coil to a different cylinder and see if the misfire follows it
- Compression test cylinder 5 — if it's significantly lower than adjacent cylinders, look for an internal engine issue rather than ignition or fuel problems
How to troubleshoot it
- Inspect and replace the cylinder 5 spark plug if worn or fouled
- Swap the cylinder 5 ignition coil with another cylinder's coil and check if the misfire code moves
- Perform a compression test on cylinder 5
- Verify the cylinder 5 injector is firing with a noid light
- Inspect intake manifold near cylinder 5 for vacuum leaks
Tools that may help
These are the types of tools commonly used when diagnosing this code. Having the right tool can save time and help confirm a diagnosis before spending money on parts.
- OBD-II scanner
- Compression tester
- Spark plug socket set
Estimated repair cost range
Spark plug: $5–$25. Ignition coil: $50–$150. Fuel injector: $100–$250. Compression test: $80–$150.
Costs vary significantly by vehicle, location, and whether you use OEM or aftermarket parts. These are general ranges for reference only.
When to call a mechanic
If you've completed the basic troubleshooting steps and the code keeps returning, or if you don't have access to the proper diagnostic tools, it's worth consulting a professional. A qualified technician can perform a full diagnosis and confirm the root cause before any parts are purchased. When in doubt, get a professional opinion — it can save you from an expensive misdiagnosis.
Real-world note
On V6 engines, cylinders 4, 5, and 6 are typically on the passenger side (Bank 2). If P0305 and P0420 (catalyst efficiency) appear together, the misfire may be damaging the Bank 2 catalytic converter.
Informational purposes only. This guide is for educational reference and is not a substitute for diagnosis by a qualified technician. Repair costs, causes, and symptoms may vary by vehicle make, model, year, and condition. Always consult a licensed mechanic before performing major repairs.