Code P0305: Cylinder 5 Misfire Detected

What is P0305?

Diagnostic trouble code (DTC) P0305 is defined as “Cylinder 5 Misfire Detected.”

This diagnostic trouble code means your engine’s powertrain control module (PCM) has detected several misfire events on cylinder 5.

How does that happen?
The cylinders in your vehicle’s engine are responsible for generating power. The fuel injector injects fuel into these cylinders, which gets combusted by a spark from spark plugs. The resulting force from the fuel combustion is what drives the crankshaft and your wheels. 

When these cylinders work together, the crankshaft’s RPM stays consistent. However, repeated misfires on any cylinder lead to a loss of engine power, rough idling, or hesitation during acceleration.

Your vehicle’s PCM constantly monitors the crankshaft’s RPM via the crankshaft position sensor signals. When it detects fluctuations in these signals due to a cylinder 5 misfire, it registers the DTC P0305 code and activates the check engine light (CEL).

7 Evident P0305 Trouble Code Symptoms

Here are some common DTC P0305 code symptoms you should look out for: 

1. Illuminated or flashing check engine light
2. The engine hesitates or jerks during acceleration
3. Lack of engine power 
4. Rough idle
5. Fuel smell from the exhaust
6. Poor fuel economy
7. Engine dying when you stop the car (rare)

10 Potential Causes of Code P0305

The most common reason for a cylinder 5 misfire is a worn-out spark plug, ignition coil, or coil pack. 

Other possible reasons for this misfire code include:

1. Faulty spark plug wire 
2. Vacuum leak 
3. Low fuel pressure due to clogged fuel injector or leaking fuel lines
4. Contaminated or old fuel 
5. A defective crankshaft position sensor
6. Engine timing off due to faulty timing belt
7. Leaking head gasket or coolant leak
8. Low engine compression 
9. Damaged hydraulic valve lifter
10. Defective PCM

NOTE: If your PCM registers other engine codes along with P0305, the causes may differ from those listed above.

Can You Still Drive With a P0305 Code?

No, you should stop driving as soon as you spot the misfire code P0305 and get it diagnosed ASAP.

P0305 code can cause your engine to run rich, which means it’ll consume more fuel than air and result in incomplete combustion. This could lead to expensive fixes, like a catalytic converter replacement. 

Additionally, repeated misfires can cause internal engine damage, such as scoring on the cylinder walls. It can cause long-term engine performance issues or the need for a full engine rebuild.

So take your car to the nearest repair shop or call a mechanic at the first sign of a problem.

How to Diagnose Code P0305

Whether you own a Toyota or a BMW, a cylinder number 5 misfire can occur due to various factors, like a bad injector. 

So, no matter how much of a DIY enthusiast you are, troubleshooting the p0305 code without proper knowledge of car parts can lead to incorrect diagnoses of this DTC code.

The solution?
Get a trusted mechanic to diagnose and resolve the P0305 trouble code for you. 

Here’s how they’ll do it:

1. Use an OBD-II scan tool to read the trouble code and the freeze frame data stored by your vehicle’s PCM. They’ll also check if any other engine code is present and fix it first.

2. Look for any loose wiring around the spark plug, ignition coil, or cylinder 5 harness. They’ll also check for a loose engine ground wire.

3. Next, check the condition of the spark plug, spark plug wire, and harness. If the spark plug or its wire is worn out, they’ll get a new plug and wire. Ideally, your mechanic will replace all the spark plugs together.

4. If your vehicle uses individual coil packs, they’ll swap the cylinder 5 coil pack with a different cylinder. If the engine misfire shifts to a different cylinder, you might have a bad coil.

5. If the spark plugs or the ignition coil are not at fault, they’ll inspect the vacuum hoses for leaks and ensure that all hoses are firmly connected. They’ll also test if the vacuum pumps work properly.

6. If there are no leaks, the mechanic will check if your engine is getting sufficient fuel. They’ll inspect the fuel pump, filter, and pressure regulator for low fuel pressure. They’ll also check the fuel injector and its wiring for damage.

7. Ensure you’re using the right fuel grade specified for your vehicle.

8. If the fuel system is working fine, perform a leakdown and compression test on your engine. These tests can help identify any mechanical problem, like a misaligned timing belt or a worn head gasket, that might be causing the misfiring cylinder.

What Are the Possible Repairs & Costs for Code P0305?

Although the P0305 error code is a generic powertrain code, its repair depends on your car’s make and model. 

Trouble code repairs usually begin with an hour of diagnosis, which may cost around $75 to $150. Once the mechanic identifies the root cause, they’ll suggest the required repairs. 

Here are some of the replacement cost estimates (including labor and parts charges) for code P0305: 

• Spark plug set: $180 to $750 
• Spark plug wire set: $220 to $605
• Ignition coil: $85 and $470 
• Vacuum pump: $570 to $620
• Fuel pressure regulator: $260 to $870
• Fuel injector: $335 to $2,000
• Fuel pump: $1100 to $1300

How to Prevent a P0305 Error Code

Here are some tips to avoid P0305 code troubles:

1. Follow routine maintenance schedules. 
2. Use high-quality fuel and avoid running the tank too low.
3. Clean the throttle body for smooth airflow.
4. Maintain steady speed, especially on highways.
5. Ensure proper oil and coolant levels.