P0305 – Cylinder 5 Misfire Detected means the engine control unit has identified that cylinder 5 is not firing correctly. A misfire in a single cylinder can lead to rough idle, lack of power, increased fuel consumption, and potential catalytic converter damage if ignored. The fault may come from ignition, fuel delivery, air metering, or mechanical engine issues. This guide explains what P0305 means, the symptoms, causes, diagnosis steps, and the most effective repair solutions to restore proper engine performance.
What Does P0305 Mean?
P0305 is a generic OBD-II code indicating that the ECU has detected repeated misfires specifically in cylinder 5. The ECU monitors crankshaft speed changes and compares cylinder contributions. When cylinder 5 produces insufficient combustion power, the ECU logs the fault.
Misfires should be repaired quickly because unburned fuel entering the exhaust stream can overheat and damage the catalytic converter, resulting in expensive repairs.
Quick Reference
- OBD-II Family: P-Code (Powertrain)
- Scope: Generic
- System: Ignition / Fuel / Air / Mechanical
- Difficulty Level: Easy–Moderate
- Estimated Repair Cost: €50–€350+
- Last Updated: 5 December 2025
Real-World Example / Field Notes
An SUV arrived with poor throttle response and noticeable shaking at idle. Misfire counters showed cylinder 5 misfiring consistently. The ignition coil showed internal resistance outside specification. Replacing both the spark plug and coil immediately resolved the misfire.
In another case, a truck developed P0305 only during heavy acceleration. The fuel injector for cylinder 5 was partially clogged, causing a lean misfire under load. Professional cleaning restored injector performance and eliminated the issue.
Symptoms of P0305 – Cylinder 5 Misfire Detected
- Rough idle: Engine vibration or shaking.
- Loss of power: Hesitation during acceleration.
- Poor fuel economy: Wasted fuel from incomplete combustion.
- Check engine light: May flash during severe misfires.
- Fuel smell: Unburned fuel entering exhaust.
- Possible stalling: Severe misfires can interrupt combustion.
Common Causes of P0305
Most Common Causes
- Worn or fouled spark plug in cylinder 5
- Faulty ignition coil or coil boot
- Clogged or leaking fuel injector (cylinder 5)
- Vacuum leak near the intake runner for cylinder 5
- Dirty or failing mass airflow (MAF) sensor
Less Common Causes
- Low compression from valve or piston issues
- Camshaft or crankshaft position sensor faults
- Weak fuel pump or failing pressure regulator
- ECU driver malfunction (rare)
- Carbon buildup affecting cylinder 5 combustion
Diagnosis: Step-By-Step Guide
To diagnose P0305 accurately, check the ignition system, fuel delivery components, vacuum integrity, and mechanical condition of cylinder 5.
Tools You’ll Need
OBD-II scanner with misfire counters, spark tester, fuel pressure gauge, compression tester, multimeter, smoke machine, and standard hand tools.
- Check freeze-frame data: Review when the misfire occurred (load, RPM, temperature).
- Inspect spark plug: Look for cracks, fouling, carbon buildup, or oil deposits.
- Swap ignition coils: Move coil 5 to another cylinder and see if the misfire follows.
- Test injector operation: Perform an injector balance test or swap injectors.
- Check for vacuum leaks: Smoke-test intake area around cylinder 5.
- Clean or test MAF sensor: Incorrect airflow readings can cause lean misfires.
- Review fuel trims: Lean trims indicate air leaks; rich trims may indicate injector issues.
- Measure fuel pressure: Ensure pump and regulator are meeting specifications.
- Perform compression test: Low compression confirms mechanical problems.
- Verify timing synchronization: Cam/crank sensor faults or timing issues may affect specific cylinders.
Pro Tip: If P0305 occurs only during high RPM or heavy throttle, suspect ignition coil breakdown — heat and voltage stress expose weak coils first.
Possible Fixes & Repair Costs
- Replace spark plug (cylinder 5): €20–€60
- Replace ignition coil: €50–€120
- Clean or replace fuel injector: €120–€250
- Repair vacuum leak: €50–€150
- Clean or replace MAF sensor: €20–€150
- Repair mechanical engine issues: €300–€900+
Can I Still Drive With P0305?
Driving with P0305 is not recommended. Unburned fuel can enter the exhaust and overheat the catalytic converter. If the check engine light is flashing, stop driving immediately to prevent severe damage.
Related Codes
- P0399 – Ignition Coil “R” Primary/Secondary Circuit
- P0364 – Reserved
- P0363 – Misfire Detected Fueling Disabled
- P0362 – Ignition Coil “L” Primary/Secondary Circuit
- P0361 – Ignition Coil “K” Primary/Secondary Circuit
- P0360 – Ignition Coil “J” Primary/Secondary Circuit
- P0359 – Ignition Coil “I” Primary/Secondary Circuit
- P0358 – Ignition Coil “H” Primary/Secondary Circuit
- P0357 – Ignition Coil “G” Primary/Secondary Circuit
- P0356 – Ignition Coil “F” Primary/Secondary Circuit
Key Takeaways
- P0305 means cylinder 5 is misfiring and requires prompt diagnosis.
- Most common causes include spark plug, ignition coil, injector, or vacuum issues.
- A flashing MIL indicates severe misfires that may damage the catalytic converter.
- Most repairs are affordable if caught early.
FAQ
What is the most common cause of P0305?
A failing ignition coil or worn spark plug is the most frequent cause of cylinder 5 misfires.
Can a vacuum leak cause P0305?
Yes. A vacuum leak near cylinder 5 can create a lean condition that leads to a misfire.
How do I know if the injector is the problem?
Perform an injector balance test or swap injectors between cylinders to see if the misfire follows.
Is it safe to drive with a cylinder 5 misfire?
No. Driving with a misfire can damage the catalytic converter and reduce engine performance.
Should I replace all ignition coils at once?
Not required, but replacing coils in sets can prevent future failures on high-mileage engines.