Code P0306: Cylinder 6 Misfire Detected

What Is P0306?

P0306 is a generic diagnostic trouble code (DTC) that means “Cylinder 6 Misfire Detected.”

Here’s a breakdown of the code:

• P – Powertrain-related issue
• 0 – Generic code (applies to all makes and models)
• 3 – Refers to the ignition system or misfire
• 06 – Indicates the problem is in cylinder 6

Your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) registers this code when it detects that cylinder number 6 is misfiring. 

Vehicles with internal combustion engines generate power by igniting a mixture of air and fuel in the engine’s cylinders. This combustion pushes the pistons, which turn the crankshaft and ultimately drive the wheels. 

An engine misfire happens when the combustion process in one specific cylinder, in this case, cylinder 6, fails. This often causes the engine speed to fluctuate, which the crankshaft position sensor detects as irregular or inconsistent rotational patterns. 

The ECM then logs the misfire code and activates the Check Engine Light.

NOTE: Most modern-day vehicles have 4, 6, or 8-cylinder engines. However, the P0306 code only applies to vehicles with six or more cylinders and explicitly denotes a misfire in cylinder 6.

Possible Causes of Code P0306

Misfires in a specific cylinder can occur for several reasons. Here are some of the most common causes of a misfire in cylinder 6:

• Worn-out spark plug, spark plug wire (also called ignition wire), or spark plug boot
• A faulty ignition coil or coil pack 
• Distributor failure
• Faulty fuel delivery system parts, such as a clogged fuel injector and fuel filter, or a broken injector connector
• Low fuel pressure
• Old or contaminated fuel 
• Vacuum leaks 
• Exhaust gas recirculation (EGR) system problems
• Bad mass air flow sensor
• Failing throttle position sensor
• Failing camshaft and crankshaft position sensor
• Engine timing off
• Mechanical engine issues like low engine compression, or leaks in the valve cover and head gasket

9 Common Symptoms of Error Code P0306

The P0306 code usually comes with a few clear warning signs, such as:

1. An illuminated or flashing Check Engine Light
2. The engine runs rough or jerks on acceleration and deceleration
3. The engine stalls when the car comes to a halt
4. Rough idling
5. Lack of engine power or engine speed
6. Trouble starting the engine
7. Fuel smell from the exhaust
8. Increased exhaust emissions
9. Decreased fuel economy

Can I Still Drive?

If your vehicle’s ECM has registered the P0306 diagnostic trouble code and you can see an illuminated or flashing Check Engine Light, you should stop driving immediately. 

A misfire is a severe car malfunction. If ignored, a misfiring cylinder could lead to ignition failure, catalytic converter damage, and several drivability issues, which can be expensive to repair. It can also cause your engine to run rich, thereby decreasing your vehicle’s fuel efficiency.

What’s more?

A misfiring cylinder releases harmful emissions, such as unburned hydrocarbons (HCs), carbon monoxide (CO), and nitrogen oxides (NOX). These toxic, odorless gases can react with sunlight to worsen air pollution.

How to Diagnose Code P0306

As noted above, there are several possible causes of a P0306 code, and a proper diagnosis can help pinpoint the exact issue to avoid costly repairs. That’s why it’s best to have a mechanic handle the diagnosis.

Here’s how they’ll diagnose the P0306 code: 

1. Use an OBD-II scanner to check for additional engine codes. If the ECM has logged other codes,  the mechanic will address them first.
2. Review freeze frame data to identify the conditions under which the misfire occurred.
3. Inspect ignition system components:
   • If the code returns and the CEL turns on, check the ignition coil and spark plug wire on cylinder number 6 for loose or damaged connections.
   • Look for signs of spark leakage from the plug wire to the ground.
4. Move the ignition coil or spark plug to a different cylinder. If the misfire follows the component, it’s likely faulty and should be replaced.
5. Check for low fuel pressure, as it can trigger a random misfire. If pressure is low, inspect the fuel injector, wiring, and injector connector for any signs of damage.
6. Examine critical engine sensors, such as the MAF, TPS, and camshaft or crankshaft position sensors. Faulty or out-of-range readings from these sensors can send incorrect signals to the ECM, leading to misfires. Replace any that are malfunctioning.
7. If the ignition and fuel system are working properly, perform compression or leak-down tests to check for mechanical issues like low compression, a leaking valve, or a blown head gasket.
8. Reset the code using the OBD-II scanner and take the vehicle for a test drive to see if the misfire returns.

Common Mistakes When Diagnosing Code P0306

When dealing with code P0306 (cylinder 6 misfire), people often make a few common errors:

• Not checking the ignition coil connection: A simple way to test a faulty ignition coil is by swapping it with one from a different cylinder. If the misfire moves to the new cylinder, the coil is likely the problem.

• Overlooking electrical connectors or hoses: Loose wires or disconnected vacuum hoses are easy to miss and can often lead to an intermittent misfire that’s harder to detect.

• Not testing parts separately: It’s important to swap one part at a time, such as the faulty fuel injector, spark plug, or ignition coil, with another cylinder. This helps determine which part is causing the issue.

Possible Repairs for P0306 & Costs

Fixing the P0306 cylinder 6 misfire code usually requires an hour of diagnostic time, for which a mechanic may charge $50 to $170.

Based on the diagnosis, here are some of the repairs or replacements that your mechanic may suggest: 

• Replace the faulty spark plug, ignition coil, or ignition wire (ideally, you should replace all the spark plugs together)
• Replace the leaking valve cover or head gasket
• Repair the vacuum leak
• Replace fuel system parts, such as a faulty fuel injector, fuel pump, fuel filter, and pressure regulator
• Replace any malfunctioning sensors, such as MAF, TPS, and camshaft or crankshaft position sensors
• Replace a faulty ECM or PCM 

Here are the average cost estimates for some of the DTC P0306 repair services (including the labor charges): 

• Vacuum leak: $12-$2,000
• Spark plugs: $50-$750
• Ignition coil: $85-$470 
• Throttle position sensor: $150-$710
• Camshaft position sensor: $185-$320
• Crankshaft position sensor: $200-$400
• Spark plug wire: $220-$605
• Mass airflow sensor: $250-$470
• Fuel pressure regulator: $260-$870
• Fuel injector: $335-$2,000
• Engine control module: $800-$1,500
• Fuel pump: $1,100-$1,300

How to Prevent a P0306 Code

To avoid a cylinder 6 misfire and keep your engine running smoothly, follow these simple tips:

• Replace a faulty spark plug on time: Follow your vehicle’s maintenance schedule, usually between 20,000 and 125,000 miles.

• Use high-quality fuel and fuel additives: They’re critical in keeping the engine components clean and preventing misfires. Periodically using fuel additives can also help clean a clogged fuel injector and avoid buildup in the fuel delivery system.

• Don’t ignore the Check Engine Light: It’s often the first warning sign of a problem, and addressing it early can help prevent severe damage and costly repairs.

• Schedule regular engine tune-ups: Routine checkups help keep all engine components working properly and reduce the risk of a random misfire.