The P0305 code triggers when cylinder #5 records a misfire. In general, misfires are cause for major concern. Not only do they reduce your engine’s power, but they can lead to long-term damage (and subsequent costly repairs).
The severity of the P0305 trouble code depends on the frequency of the misfires and their ultimate cause. Use the steps below to help you diagnose the problem before it becomes more serious.
P0305 Code Definition
P0305 Code Definition (Generic): Cylinder #5 Misfire Detected
P0305 BMW Code Definition: #5 Cylinder Miss Fire
P0305 Ford Code Definition: Fault Cylinder ‘E’ – Misfire Detected
P0305 Nissan Code Definition: Cylinder #5 Misfire Detected
What Does P0305 Mean?
The cylinders in your engine are what produces the power. Fuel is injected into the cylinder and is combusted by the spark from the spark plug. The energy released in the combustion turns the crankshaft, generating power.
The cylinders in your engine work together to provide constant power to the crankshaft. When things are working correctly, they fire in sequence so smoothly the crankshaft’s RPM is consistent. A single misfire won’t have much impact on your system. Repeated or chronic misfires, however, will lead to significant loss of engine power.
Code P0305 triggers when the #5 cylinder misfires. On Fords, this is defined as Cylinder ‘E’. You’re likely to see it in combination with P0300, the general misfire code. Driving with a misfiring engine can damage its internal components, so this isn’t a code you want to ignore.
What Are The Symptoms Of The P0305 Code?
You can use the symptoms present with the P0305 code to guide your diagnosis. The most common symptoms include:
- Activation of the check engine light. If the light is solid, the misfire may be random or sporadic. A flashing check engine light indicates repeated misfires and is cause for more concern.
- Rough idle
- Hard starts
- Shaking or stumbling engine
- Jerks and hesitations during acceleration
- Reduced engine power
- Fuel odors in the exhaust
What Are The Causes Of P0305?
The most common causes of the P0305 OBD2 code are:
- Faulty or worn-out spark plugs
- Faulty wiring around the spark plugs
- Faulty ignition coils
- Faulty fuel injector
- Failed distributor
Other possible causes include:
- Leaks in the vacuum system
- Low fuel pressure
- Defective camshaft or crankshaft sensor
- Engine timing issues
- Faulty catalytic converter
- Fuel quality too low
- Fuel level too low
How Serious Is The P0305 Code?
The P0305 OBD2 code is very serious. The drivability issues associated with the code can make it unsafe to operate your vehicle. Repeated misfires can also cause long-term engine damage. Stop driving your car immediately and don’t use it again until you’ve repaired the cause.
How To Diagnose And Fix The P0305 Code
If the check engine light is solid and there are no drivability issues, clear the codes and test drive your car. The code may not return if the misfire was an isolated incident. Monitor your engine performance and continue with repairs if the code returns.
Tools you’ll need:
- OBD2 scan tool
- Basic tool kit (screwdriver, a ratchet set, socket set, etc.)
- Digital multimeter
- Fuel pressure gauge
- Compression tester
- Read the freeze frame data using the OBD2 scanner. Identify the conditions in which the code initially triggered. If any other trouble codes are present, fix those first, as that may be the root cause of the misfire.
- Check the wiring around the spark plugs and wiring harness. Re-connect any that are loose, and replace any that are frayed or damaged.
- Inspect the vacuum hoses in your engine for damage and leaks, feeling for issues in any hidden areas. If you find any leaking hoses, replace them. Pay close attention to the ends, as well, and ensure they’re firmly connected.
- If you have individual coil packs, swap the cylinder 5 pack with the cylinder 4 pack. Clear the codes then test drive and scan your vehicle. If the misfire moved to cylinder 4, you’ve identified the coil pack as the issue. Replace the coil pack, clear the codes, and test your vehicle again.
- Inspect the spark plugs. If they’re shiny with oil, carefully wipe them clean and replace them. Replace any spark plugs with black carbon build-up or visible corrosion.
- Test the spark plug wires with a digital multimeter. Remove each wire, connecting each multimeter lead to an end. Compare it with the specified reading in your vehicle’s manual. If more than 2 wires fail, replace the entire harness.
- Perform a compression test to check for mechanical issues. Burned valves, worn valve guides, and similar mechanical failures can lead to misfires.
- Check the timing chain. Ensure it’s properly aligned and that it hasn’t skipped any teeth.
- Verify that you’re using the grade of fuel specified in your vehicle’s manual. While this is a rare cause of the P0305 trouble code, issues with the fuel quality can cause misfires. If the fuel is incorrect, drain and flush your system, then refill it with the correct fuel type.
- Use a digital multimeter to check the fuel injectors. If the reading doesn’t match the specifications in your vehicle’s manual, replace them.
- Should the P0305 code return, the issue is most likely with your fuel system. Check the fuel pressure with a fuel pressure gauge. If it’s too low, your fuel pump may be failing. Take your vehicle to a mechanic for further diagnosis.
Common Mistakes To Avoid While Diagnosing The P0305 Code
Many mechanics immediately replace the spark plug or ignition coils when a misfire code triggers. While these are often the cause, you want to conduct a thorough diagnosis before jumping to any conclusions.
Tips To Avoid P0305 In The Future
Many times, misfires are caused by issues with the air-to-fuel ratio. Leaks in the vacuum system can cause these, as can be clogged or leaking components in the exhaust system. Periodic inspection of the hoses, wires, and valves in your system can help you stop problems before they happen.