The P0305 is one of several misfire codes you can read on your scan tool. I studied 120+ different vehicles with misfires and how were they fixed, to provide you with a list of the most common causes, also with an action plan to diagnose this fault in no time.
You don’t want to delay fixing your P0305 as the misfire will damage your catalytic converters or engine internals. Both of these fixes are priced at thousands of dollars while the misfire is often caused by a worn-out $5 spark plug. Fix it ASAP.
P0305 quick overview
| Meaning | P0305: Cylinder #5 Misfire Detected |
| Is it serious? | Yes, this code is serious and should be addressed immediately to prevent further damage to the engine or catalytic converter. |
| Possible causes | -Worn or faulty spark plug in cylinder #5 -Defective ignition coil for cylinder #5 -Malfunctioning fuel injector for cylinder #5 -Vacuum leak affecting cylinder #5 -Timing issues (e.g., camshaft timing off by one tooth) -Internal engine issues (e.g., valve problems or piston ring wear) -Wiring or electrical connection problems related to cylinder #5 |
| How to diagnose? | Inspect Spark Plug: Check the spark plug in cylinder #5 for signs of wear or fouling. Test Ignition Coil: Swap the ignition coil with another cylinder to see if the misfire follows. Check Fuel Injector: Perform a swap or test of the fuel injector in cylinder #5 to ensure it’s functioning correctly. Inspect Vacuum System: Check for vacuum leaks, especially around the PCV valve and related components. Perform Compression Test: Conduct a compression test on cylinder #5 to rule out internal mechanical issues. Inspect Timing Components: Examine the timing belt and related components for misalignment or damage. Inspect Wiring: Examine wiring and connections related to cylinder #5 for any faults or loose connections. |
P0305 Meaning
The P0305 code shows that your car’s engine isn’t burning fuel properly in cylinder #5. This can cause the engine to run poorly and might lead to more expensive damage if not fixed soon. Start by checking the spark plug, ignition coil, and fuel injector in that cylinder.
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Case study: real cases of solving P0305
I checked specifically for code P0305 and picked these example fixes from my full case study of 123 vehicles with misfires.
How to fix P0305 on Ford
Car: 2001 Ford Escape XLS
Problem: P0305
Diagnosing: Replacing the ignition coils didn’t help, but the found was found on the wiring harness to the ECU.
Fix: Fix the wiring harness
How to fix P0305 on Honda
Car: 2001 Honda Accord EX 3.0L
Problem: Misfire, P0300, P0301 – P0305
Diagnosing: The technician tried to swap to coils around but the codes stayed the same, but he couldn’t find another issue since he checked the fuel, timing, and compression and also ruled out vacuum leaks.
Fix: All ignition coils were bad, fixed by replacing them. (that’s why it didn’t show on “swap test”)
How to fix P0305 on Volkswagen
Car: 2006 Volkswagen Touareg 3.2L
Problem: Misfire, P0300, P0301 – P0304, P0305
Diagnosing: The misfire was happening at low RPM, and the idle was poor quality signaling the misfire is most likely caused by a vacuum leak.
Fix: Replacing the PCV valve fixed the issue (stuck-open PCV caused an internal vacuum leak)
How to fix P0305 on KIA
Car: 2007 Kia Rondo LX 2.7L
Problem: Misfire, P0301, P0303, P0300, P0305, check engine light flashing
Diagnosing: Misfire codes are telling us that the fault will be caused by something affecting 1 whole Bank (1, 3, 5 cylinders are all in BANK1). The issue was found in camshaft timing (off by 1 tooth).
Fix: Fix the timing issue
How to fix P0305 on BMW
Car: 2006 BMW 650i 4.8L
Problem: No Start, Stall, Misfire, P0300 – P0305
Diagnosing: The car was able to start for 10-20 running extremely rough when you give it a gas and then dying. The technician drained the fuel tank discovering contaminations in the gas.
Fix: Fuel system clean, new good gas
The key takeaways from these cases
- Negative fuel trims mean it is trying to correct for a rich condition. Maybe the coolant temperature sensor is sending false info to the PCM. May also be a bad map sensor.
- Remember that new aftermarket (even OEM) parts can come faulty. Don’t forget that in your diagnosing process
P0305 FAQ and conclusion:
Check the Wikipedia article on combustion engines if you are still unsure what exactly the misfire is. Understanding it will help you with your diagnosis.
The key takeaways from these cases
- Don’t change coils/spark plugs unless you confirm they are faulty (do a swap test at least)
- A lot of misfire cases are caused by internal engine damage/timing so don’t rush with replacing ignition/fuel parts without further diagnosis
- Your diagnosing is sometimes right, but only the OEM part will solve the issue
OBD-II scanner Buyer’s Guide
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I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko