The OBD-II code P0305 means that the powertrain control module (PCM) has detected a misfire in one of the engine’s cylinders. It usually stems from a problem with the ignition system, fuel system, or internal engine components.
Read this guide to learn more about the P0305 error code—what it means, its symptoms and causes, as well as tips for diagnosis and repair.
What Does the Code P0305 Mean?
Diagnostic trouble code (DTC) P0302 stands for “Cylinder 5 Misfire Detected.” This means that the powertrain control module (PCM) has detected a misfire on cylinder 5.
A misfire happens when something impedes or disrupts the combustion process inside the cylinder. In the case of the P0305 code, it means that cylinder 5 is not firing as it should. For engine misfire codes, the last digit usually indicates the specific cylinder that’s causing problems.
For P0305, the misfire is taking place in the 5th cylinder. If you get a code P0303, the error should be in the 3rd cylinder, and so on.
Modern vehicles come with a computer called the Engine Control Unit (ECU) or the PCM. These computers work with a system of sensors around the car to detect problems.
If a misfire happens, your car’s computer alerts you by triggering the check engine light.
The misfire monitor relies heavily on the crankshaft position sensor signal. Your vehicle’s PCM determines a misfire via the crankshaft sensor and, in some cases, the camshaft sensor.
Whenever a cylinder misfires, it slows down a bit. The camshaft and crankshaft sensors detect the slowdown, and the PCM calculates it. That’s why a faulty crankshaft position sensor can misdiagnose misfires.
What are the Possible Causes of the P0305 Code?
A thorough diagnosis can pinpoint the exact cause of code P0305. Common causes of the code include:
- Ignition system problems (e.g.a worn spark plug or failed coil pack)
- Fuel system problems (e.g., failed fuel injector or damaged injector driver)
- Engine mechanical problems (e.g., a leaking valve or damaged lifter)
Note: If there are other codes stored in addition to P0305, the causes and symptoms may differ from those listed here.
What are the Common Symptoms of the P0305 Code?
Below are the most common symptoms that accompany the error code P0305 or a cylinder 5 misfire:
- Check engine light
- Hesitating, stumbling, and jerking as you accelerate
- Lack of power during acceleration
- Rough idling
- Dying at stop signs
- Poor fuel economy
How to Diagnose the P0305 Code
Because there are so many potential causes for code P0305, diagnosis can be difficult. The root cause of the problem could be anything from a worn spark plug to a costly internal engine concern.
Hence, it’s a good idea to check for technical service bulletins (if you have access) that could help with the troubleshooting process.
Below are a couple of video references you can use to help you perform a diagnosis
How to Fix the P0305 Code
Due to the diversity of vehicle models and the different conditions that can trigger code P0305, there isn’t really a universal solution for this issue—which can make it difficult to address the problem, especially if you’re not an expert.
If you’re confident enough to resolve the P0305 code on your own, make sure to consult the factory repair information to ensure the suitability of your repair approach. Use repair manuals or, better yet, invest in an ALLDATA single-vehicle subscription to expand your technical know-how.
When in doubt, don’t hesitate to reach out to your trusted mechanic. They’ll be able to help you pinpoint the exact cause of the issue and determine the best course of action.