Ignition and misfire
P0305 — Cylinder 5 Misfire Detected
The engine computer (ECU/PCM) has detected that cylinder 5 is not burning its air-fuel mixture properly. The engine runs rough, loses power and uses more fuel, and unburned fuel can overheat and damage the catalytic converter.
What is specific to cylinder 5
P0305 points at cylinder 5 only; the other cylinders are still firing normally. The fault is therefore usually in a part that belongs to that cylinder, such as the spark plug, ignition coil, injector or compression, and rarely in something shared by the whole engine. Cylinder numbering differs between engines, so identify cylinder 5 from the manufacturer's documentation before removing anything.
- Swap the cylinder 5 ignition coil with another cylinder's coil, clear the code and run the engine: if the code follows to the other cylinder, the coil is the culprit.
- Inspect or replace the cylinder 5 spark plug and compare its colour and wear with the other plugs.
- If the plug and coil are good, test compression on cylinder 5 and check that the cylinder 5 injector is working.
Common causes
- Worn or fouled spark plug
- Failing ignition coil or coil connector on cylinder 5
- Clogged or leaking fuel injector on cylinder 5
- Vacuum leak or intake gasket leak near the cylinder
- Low compression (worn rings, burnt valve, head gasket)
- Damaged spark plug wire (on engines that use them)
Symptoms
- Rough idle and engine shaking
- Loss of power when accelerating
- Flashing or steady check engine light
- Fuel smell from the exhaust and higher fuel use
How to check
- Read freeze-frame data and check whether other misfire codes are stored
- Inspect the spark plug of cylinder 5 and compare it with the others
- Swap the ignition coil of cylinder 5 with a healthy cylinder and see whether the code follows the coil
- Check injector operation and fuel trims, then look for vacuum leaks
- If the ignition and fuel side are good, run a compression or leak-down test
Can you keep driving?
Driving a short distance is usually possible, but avoid hard loads. If the check engine light flashes, stop and do not keep driving: raw fuel can quickly ruin the catalytic converter.
How this differs from P0300
P0300 reports a random or multi-cylinder misfire and points to shared causes such as a lean mixture, low fuel pressure or a vacuum leak. P0305 names cylinder 5, so start with the parts of that cylinder. If the scan tool shows both P0300 and P0305, the shared causes still need to be ruled out.
Codes in the same family
P0300 to P0308 all describe misfires: P0300 is a random or multiple-cylinder misfire, while P0301 to P0308 name cylinder 1 to cylinder 8.
Related codes
Frequently asked questions
- What does code P0305 mean?
- P0305 means the ECU detected misfires in cylinder 5: the mixture in that cylinder is not burning completely.
- Is it safe to drive with P0305?
- For a short trip at light load it is usually possible, but a flashing check engine light means active heavy misfire and you should stop and have the car checked.
General reference information. It does not replace a diagnosis on your own vehicle. The same code can have different causes depending on make, model year and engine; check the manufacturer's documentation or ask a technician with a scan tool.