P0305 Code: Cylinder 5 Misfire Detected
If your scanner returned the P0305 code, your engine control module has detected a misfire specifically in cylinder 5. Just like P0304 points to cylinder 4, the P0305 code gives you a precise location to start your diagnosis.
The P0305 code appears most commonly on 6-cylinder and 8-cylinder engines — because 4-cylinder engines only have four cylinders. If you’re seeing this on a 4-cylinder, double-check the code. On V6 and V8 engines, cylinder 5 is often on the rear bank, which can make access a little more involved than the front cylinders.
A misfire means the air-fuel mixture in cylinder 5 isn’t combusting properly. The engine drops a power stroke every time it happens, and you feel it — rough idle, vibration, hesitation. The cause is almost always the spark, the fuel, or the compression.
What You’ll Notice
- Check engine light on — possibly flashing
- Rough or uneven idle
- Engine vibration, especially noticeable at a standstill
- Hesitation or stumble when pressing the accelerator
- Loss of power, particularly at lower RPM
- Increased fuel consumption
- Smell of unburned fuel from the exhaust in severe cases
A flashing check engine light with the P0305 code means the misfire is happening right now and is actively damaging the catalytic converter. Don’t drive further than necessary.
Where Is Cylinder 5?
- Inline 6-cylinder: Fifth cylinder from the accessory belt end
- V6 engines: Usually the middle or rear cylinder on one of the banks — check your service manual
- V8 engines: Typically on the passenger side bank — position varies by manufacturer
On V-configuration engines, cylinder 5 can be on either bank depending on the make. Always confirm the location in your vehicle’s service manual before pulling components.
What Usually Causes the P0305 Code
1. Worn or fouled spark plug The most common cause of the P0305 code. A worn plug produces a weak, unreliable spark. A plug contaminated with oil or carbon fails to fire consistently. Start here every time — it’s the cheapest fix and resolves P0305 more often than anything else.
2. Failed ignition coil on cylinder 5 On coil-on-plug engines, each cylinder has its own coil. When cylinder 5’s coil weakens or fails, the spark it delivers becomes inconsistent. The coil swap test — the same method used for P0301 through P0304 — confirms whether the coil is the problem in minutes.
3. Faulty fuel injector on cylinder 5 A clogged injector can’t deliver enough fuel. A dead injector causes a complete misfire on every cycle. If the plug and coil check out, the injector is next.
4. Low compression in cylinder 5 A burnt valve, worn piston rings, or a head gasket issue affecting cylinder 5 drops compression below what combustion needs. Replacing the plug or coil won’t fix a compression problem — the P0305 code comes straight back.
5. Vacuum leak near cylinder 5 A cracked intake manifold gasket or split vacuum hose near cylinder 5 introduces unmetered air, leaning out the mixture in that cylinder. Typically worse at idle and improves at higher RPM.
6. Wiring fault A damaged or corroded wire on the coil or injector circuit for cylinder 5 can cause an intermittent or permanent misfire. Less common, but worth checking when mechanical components test fine.
How Serious Is the P0305 Code?
Serious — don’t put it off.
Unburned fuel from a misfiring cylinder enters the exhaust and burns inside the catalytic converter. Every misfire cycle accelerates converter damage. On 6 and 8-cylinder engines, a misfiring cylinder also means the remaining cylinders work harder to compensate — adding wear across the engine.
Fix it early and it’s usually a simple repair. Leave it and the catalytic converter eventually fails — at a significantly higher cost.
How to Diagnose the P0305 Code
Step 1 — Read all stored codes
Confirm P0305 and check for companion codes. P0300 alongside P0305 means cylinder 5 is the main problem but the misfire may be widespread. A standalone P0305 means the fault is isolated to cylinder 5.
Step 2 — Pull the cylinder 5 spark plug
Remove it and compare it to plugs from the other cylinders. A plug that looks different — fouled, blistered, oil-coated, or heavily worn — points to a specific problem in cylinder 5. Replace it and retest before going further.
Step 3 — Swap the ignition coil
Move cylinder 5’s coil to another cylinder. Clear all codes and drive. If the misfire code follows the coil to its new cylinder, the coil is causing the P0305 code. If P0305 stays on cylinder 5, the coil is fine.
Step 4 — Test the fuel injector
Listen to cylinder 5’s injector with a mechanic’s stethoscope while the engine runs. A healthy injector clicks rhythmically. Check resistance with a multimeter and compare to specification. A dead or out-of-spec reading confirms a fuel delivery problem.
Step 5 — Check for vacuum leaks
Carefully spray carburetor cleaner around the intake manifold gasket and vacuum lines near cylinder 5 while the engine idles. A change in idle at a specific spot pinpoints the leak. A smoke test gives you a more complete picture.
Step 6 — Compression test
If plugs, coil, and injector all check out, test cylinder 5’s compression. A reading significantly lower than the other cylinders — or below manufacturer’s minimum — means an internal engine fault is behind the P0305 code.
How to Fix the P0305 Code
Replace the spark plug — Always start here. Replace the cylinder 5 plug and inspect the others. On a high-mileage engine with original plugs, replace the full set.
Replace the ignition coil — Confirmed by the swap test. Fit a new coil — don’t swap the old one back.
Clean or replace the fuel injector — A quality fuel system cleaner handles mild clogging. A confirmed failed injector needs replacement.
Repair vacuum leaks — Replace cracked hoses and failed gaskets. More labor on some V-configuration engines, but the parts are inexpensive.
Engine repair — If low compression is the root cause, the repair path depends on what’s causing it. A burnt valve requires head work. Worn rings mean more extensive engine attention. Get a proper diagnosis before committing to this repair.
What It Might Cost to Fix the P0305 Code
| Repair | Estimated Cost |
|---|---|
| Spark plug replacement | $20 – $200 |
| Ignition coil replacement | $80 – $350 |
| Fuel injector cleaning | $50 – $150 |
| Fuel injector replacement | $150 – $400 |
| Vacuum leak repair | $100 – $400 |
| Head work / engine repair | $500 – $2,500+ |
V6 and V8 engines can cost more due to additional labor. Costs vary by vehicle make, model, and labor rates in your area.
Related Codes
- P0300 — Random/Multiple Cylinder Misfire Detected
- P0301 — Cylinder 1 Misfire Detected
- P0302 — Cylinder 2 Misfire Detected
- P0303 — Cylinder 3 Misfire Detected
- P0304 — Cylinder 4 Misfire Detected
- P0306 — Cylinder 6 Misfire Detected
- P0355 — Ignition Coil E Primary/Secondary Circuit Malfunction
- P0205 — Injector Circuit Malfunction Cylinder 5
Frequently Asked Questions
Can I drive with the P0305 code? With a steady light and manageable symptoms, short necessary trips are possible. But every kilometre on a misfire damages the catalytic converter. If the light is flashing, minimize driving immediately.
My car is a 4-cylinder and I got P0305 — is that possible? P0305 on a 4-cylinder engine is unusual. Double-check the code with a reliable scanner. Some aftermarket readers misread codes. If P0305 is confirmed on a 4-cylinder, the issue may be with the ECM itself rather than a physical cylinder.
How do I diagnose P0305 if cylinder 5 is hard to reach? Start with the coil swap test — it doesn’t require you to access cylinder 5 directly. Move the coil from cylinder 5 to an accessible cylinder and see if the misfire follows. If it does, you know the coil is the problem before wrestling with difficult access.
P0305 keeps coming back after replacing the plug. What now? Move to the coil swap test. If the misfire follows the coil, replace it. If it stays on cylinder 5, test the injector and check for vacuum leaks. A persistent P0305 after plug and coil replacement often points to a fuel delivery or compression issue.
Does P0305 affect all engine types the same way? The code means the same thing across all engines, but the symptoms can feel different. On a V8, one misfiring cylinder out of eight is less noticeable than on a 6-cylinder. That can make it tempting to ignore — but the catalytic converter damage accumulates the same way regardless of engine size.
This guide is for informational purposes only. For an accurate diagnosis, always consult a qualified mechanic.
