P0306 on a Honda Accord V6: What the Code Means and How to Fix It

P0306 on a Honda Accord V6 means the engine control module has detected a misfire in cylinder 6. In practical terms, one cylinder isn’t firing correctly, which can cause rough running, reduced power, and potential catalytic converter damage if ignored. On most Accord V6 models (Honda’s J‑series engines), cylinder 6 is on the front bank (radiator side), typically the cylinder nearest the driver side in left-hand-drive vehicles.

What P0306 Signals on the Accord V6

P0306 is an OBD-II misfire code specific to cylinder 6. The powertrain control module identifies a misfire by monitoring crankshaft speed fluctuations; when one cylinder contributes less torque than expected, it flags that cylinder. While the code pinpoints the affected cylinder, it doesn’t by itself tell you why it’s misfiring.

Locating Cylinder 6

On the transverse-mounted Honda V6 (J30/J32/J35 found in Accord V6 models), the front bank faces the radiator and contains cylinders 2-4-6 from passenger to driver side. Cylinder 6 is thus the front-bank cylinder closest to the driver side in most North American, left-hand-drive Accords. Always confirm with your service manual for your specific model year and market orientation.

Symptoms You May Notice

The following list outlines common symptoms that accompany code P0306 on a Honda Accord V6, helping you recognize the issue before diagnostics begin.

• Rough idle, shaking, or vibration, especially at stoplights
• Reduced power, hesitation, or stumbling under load
• Check Engine Light on; it may flash under heavy misfire
• Increased fuel consumption and fuel smell from exhaust
• Possible popping from exhaust or sulfur/rotten-egg odor if the catalytic converter is stressed

These symptoms vary with severity; an intermittent misfire may only be noticeable at idle or during light cruise, while a consistent misfire will affect drivability across conditions.

Common Causes on Accord V6 Engines

Several issues can trigger a cylinder-specific misfire on the Accord V6. This list prioritizes common, Accord-specific patterns before moving to less frequent mechanical causes.

• Worn, fouled, incorrectly gapped, or wrong-type spark plug in cylinder 6 (use the exact NGK or Denso plug specified by Honda)
• Failing ignition coil on cylinder 6, or moisture/oil contamination in the plug tube
• Fuel injector fault on cylinder 6 (clogged, weak, stuck, or wiring/connector issues)
• Vacuum leak or intake manifold gasket leak near the cylinder 6 runner
• Oil in spark plug tubes from leaking tube seals or valve cover gasket
• Low compression from a burnt valve, worn rings, or head gasket issue (less common but critical to check if ignition and fuel are good)
• Engine control updates or Variable Cylinder Management (VCM) side effects on some model years leading to plug fouling and oil consumption (Honda issued TSBs and extended warranties on certain VCM-equipped models; cylinder 6 can still misfire from standard causes even if VCM issues often affect other cylinders)
• EGR-related deposits causing distribution imbalance (less common for a single-cylinder code but possible)

Start with the highest-probability items—spark plug and coil—then proceed to fuel delivery and mechanical integrity to pinpoint the root cause efficiently.

How to Diagnose P0306

A systematic approach prevents guesswork and unnecessary parts replacement. The steps below reflect common dealership and professional workflows for Honda V6 engines.

1. Scan and record data: Read all codes and freeze-frame data. Note engine load, RPM, fuel trims, and misfire counters. Address any companion codes (e.g., fuel trim or multiple misfires) that could steer diagnostics.
2. Visual inspection: Check cylinder 6 coil connector, wiring, and the plug tube for oil or coolant contamination. Inspect grounds and look for obvious vacuum leaks at the front bank near cylinder 6.
3. Spark plug check: Remove the cylinder 6 plug. Examine for wear, cracks, oil fouling, ash deposits, or improper gap. Replace with the exact Honda-specified plug type and heat range if needed. Torque per Honda spec (commonly around 13 lb-ft/18 N·m for 14 mm threads, but verify for your model).
4. Coil “swap test”: Swap the cylinder 6 ignition coil with another cylinder. Clear codes and test drive. If the misfire code follows the coil (e.g., becomes P0304), the coil is bad.
5. Injector evaluation: Use a stethoscope to confirm injector clicking on cylinder 6. If accessible, swap injectors between cylinders or perform an injector balance test. Check injector wiring with a noid light if needed.
6. Fuel and air checks: Review short- and long-term fuel trims at idle and 2,500 rpm. Excessively positive trims suggest vacuum/intake leaks; smoke-test the intake manifold and PCV system, especially near the cylinder 6 runner.
7. Mechanical health: Perform a compression test; follow with a leak-down test if compression is low. Listen for air escaping from intake, exhaust, or crankcase to identify valves, rings, or head-gasket issues.
8. Software/TSB review: For VCM-equipped years, check for Honda PCM updates or TSBs addressing misfires and oil consumption. Apply updates as applicable.
9. Final verification: After repairs, clear codes and road test while monitoring misfire counters and fuel trims to ensure the condition is resolved.

This progression isolates ignition, fuel, air, and mechanical causes logically, reducing parts cannon fixes and confirming the repair with data.

Can You Keep Driving?

Brief trips at light load may be possible, but extended driving with an active misfire risks overheating and damaging the catalytic converter. If the check-engine light flashes, reduce load immediately and arrange service; a tow is prudent if the engine runs very rough.

Estimated Repair Costs

Costs vary by region and model year, but these ranges reflect typical parts and labor for Accord V6 misfire repairs.

• Diagnostic fee: $120–$200
• Spark plug (each, correct OEM type): $10–$25; full set replacement adds labor
• Ignition coil (each): $60–$140 plus 0.3–0.6 hr labor per coil
• Fuel injector (each): $120–$250 plus 1.5–3.0 hr labor depending on access
• Valve cover/tube seals: $150–$350 parts and labor if oil is in plug tubes
• Intake manifold gasket/leak repair: $150–$400
• Compression-related repairs (valve work/head gasket): varies widely, $1,200+

Accurate diagnosis up front saves money by targeting the faulty component rather than replacing multiple parts.

Prevention and Maintenance Tips

Preventing misfires extends catalytic converter life and keeps the V6 running smoothly. These steps reduce the likelihood of P0306 returning.

• Use only Honda-specified NGK or Denso spark plugs; replace at the recommended interval
• Keep oil changes on time and monitor oil consumption, especially on VCM-equipped models
• Replace the PCV valve at recommended intervals to limit oil ingestion
• Avoid pressure-washing the engine bay, which can force moisture into coils
• Use Top Tier fuel; periodic high-quality injector cleaner can help keep injectors clear
• Address vacuum leaks promptly and ensure intake gaskets and hoses are in good condition
• Check for and apply relevant Honda software updates and TSBs

Consistent maintenance and prompt attention to early signs of misfire help prevent more costly damage down the line.

Summary

P0306 on a Honda Accord V6 indicates a misfire in cylinder 6, typically the front-bank, driver-side cylinder. Most fixes center on the spark plug, ignition coil, injector, or an intake leak near that runner; mechanical issues are less common but critical to rule out with compression testing. Diagnose methodically—inspect, swap-test, verify fuel and air, then assess mechanical health—and avoid prolonged driving to protect the catalytic converter. With the right parts and procedures, most P0306 issues are straightforward to resolve.

What is the most common cause of the P0306 code?

The most common causes of a P0306 code, indicating a misfire in cylinder 6, are faulty ignition system components (spark plug, spark plug wire, or ignition coil), fuel delivery problems (clogged fuel injector), or vacuum leaks. Other potential causes include low engine compression, a dirty Mass Airflow (MAF) sensor, or an exhaust gas recirculation (EGR) system malfunction. 
Ignition System Issues

• Spark Plug: . Opens in new tabA worn-out, fouled, or damaged spark plug in cylinder 6. 
• Spark Plug Wire/Boot: . Opens in new tabA damaged or leaking spark plug wire or boot can cause the spark to ground out prematurely. 
• Ignition Coil: . Opens in new tabA faulty ignition coil for cylinder 6 may not be firing the spark plug correctly. 
• Distributor Cap/Rotor: . Opens in new tabIf your vehicle has a distributor, a faulty cap or rotor can cause ignition problems. 

Fuel System Issues

• Fuel Injector: . Opens in new tabA clogged or malfunctioning fuel injector for cylinder 6 can prevent the correct amount of fuel from being delivered. 
• Low Fuel Pressure: . Opens in new tabInsufficient fuel pressure in the fuel system can lead to a lean air-fuel mixture, causing misfires. 

Air Intake & Vacuum Leaks

• Vacuum Leak: . Opens in new tabA leak in a vacuum hose or component can allow unmetered air into the engine, disrupting the air-fuel ratio and causing a misfire. 
• Dirty MAF Sensor: . Opens in new tabA dirty Mass Airflow (MAF) sensor can provide incorrect air readings to the engine control module (ECM), leading to an improper fuel mixture. 

Mechanical Engine Problems

• Low Engine Compression: . Opens in new tabIssues like worn piston rings or faulty valves can result in low compression in cylinder 6, leading to incomplete combustion. 
• Leaking Head Gasket: . Opens in new tabA torn head gasket can allow coolant, oil, or air into the combustion chamber, interfering with proper ignition. 
• EGR System Malfunction: . Opens in new tabA problem with the exhaust gas recirculation system can also cause a misfire. 

Troubleshooting Steps

1. 1. Inspect the basics: Check the spark plug, plug wire, and ignition coil for cylinder 6 for damage. 
2. 2. Swap components: Try swapping the ignition coil and spark plug from cylinder 6 to another cylinder to see if the misfire moves with the component. 
3. 3. Check for leaks: Look for any obvious vacuum leaks or signs of oil leaking into the spark plug hole. 
4. 4. Perform tests: A professional technician can perform a compression test and check fuel pressure and injector function. 

What is the most common cause of cylinder 3 misfire?

What Causes P0303?

• Faulty coil.
• Faulty fuel injector.
• Faulty oxygen sensor.
• Poor compression.
• Burned exhaust valve.
• Low or no Fuel.

How do I fix code P0306?

Code P0306 indicates a misfire in cylinder #6. To fix it, you’ll need to diagnose and potentially replace faulty components like the spark plug, ignition coil, or fuel injector for that cylinder. You might also need to address vacuum leaks or internal engine issues if they are present. 
Here’s a more detailed breakdown of potential causes and fixes:
1. Spark Plug:

• A worn or fouled spark plug in cylinder #6 is a common cause of misfires. 
• Fix: Replace the spark plug, and consider replacing all spark plugs if they are all old. 

2. Ignition Coil:

• The ignition coil for cylinder #6 may be faulty. 
• Fix: Inspect the coil for damage (cracks, etc.) and replace it if necessary. You can also swap the coil with another cylinder to see if the misfire follows the coil. 

3. Fuel Injector:

• A clogged or malfunctioning fuel injector for cylinder #6 can also cause a misfire. 
• Fix: Check the injector’s spray pattern and resistance. Consider cleaning or replacing it if necessary. 

4. Vacuum Leaks: 

• Leaks in the intake manifold or vacuum lines near cylinder #6 can disrupt the air-fuel mixture and cause a misfire.
• Fix: Inspect for leaks and repair or replace damaged components.

5. Internal Engine Issues: 

• In some cases, internal engine problems like worn piston rings, valve issues, or low compression can lead to misfires.
• Fix: These issues typically require more extensive repairs or engine work.

Troubleshooting Steps:

1. Check the spark plug and ignition coil for cylinder #6: Inspect them for damage or wear. 
2. Consider swapping components: Swap the ignition coil and spark plug with another cylinder to see if the misfire follows the component. 
3. Inspect for vacuum leaks: Carefully check around the intake manifold and vacuum lines for any signs of leaks. 
4. Test fuel injector: If the issue persists, test the fuel injector for proper operation. 
5. Consider internal engine issues: If the problem persists, consult a professional for further diagnosis. 

Important Considerations:

• Always refer to your vehicle’s repair manual for specific instructions and torque specifications. 
• If you are not comfortable performing these repairs, consult a qualified mechanic. 
• Clearing the code after repairs is essential to verify that the issue has been resolved, according to some automotive resources. 

How to fix misfire cylinder 6?

A misfire in cylinder 6, indicated by the P0306 trouble code, often stems from issues with the ignition system, fuel delivery, or air intake. To address it, first check and potentially replace the spark plug and ignition coil for cylinder 6. Inspect for loose connections in the ignition and fuel systems. Consider a compression test to rule out internal engine problems. If those are fine, check for vacuum leaks, which can disrupt the air-fuel mixture. Finally, if the problem persists, consider inspecting the fuel injector for proper operation. 
This video demonstrates how to fix a P0306 engine code by checking and replacing the spark plug: 54snondaYouTube · Oct 22, 2020
Here’s a more detailed breakdown:
1. Check Ignition System: 

• Spark Plug: Replace the spark plug in cylinder 6, or replace all spark plugs as a set if they are due for replacement. 
• Ignition Coil: Inspect the ignition coil for cylinder 6 for any signs of damage, such as cracks, and replace it if needed. 
• Connections: Ensure all connections in the ignition system, including the coil and spark plug, are secure and free of corrosion. 

2. Check for Vacuum Leaks: 

• Smoke Test: Use a smoke machine or carburetor cleaner to check for leaks around the intake manifold, vacuum hoses, and seals.
• Identify Leaks: If the engine idle speed changes when spraying the cleaner, it indicates a leak, which should be sealed. 

3. Inspect Fuel Injector: 

• Clicking Sound: Listen for a clicking sound from the fuel injector, which indicates it is operating. If no sound is heard, the injector may be clogged or malfunctioning. 
• Replacement or Cleaning: If the injector is faulty, it may need to be cleaned or replaced. 

4. Compression Test:

• Low Compression: A compression test can help determine if the misfire is caused by low compression, potentially indicating a problem with piston rings or a damaged cylinder head. 
• Further Diagnosis: If low compression is found, further disassembly and repairs may be necessary. 

This video explains the possible causes of a P0306 code, including vacuum leaks and dirty throttle plates: 1mCar FixYouTube · Mar 22, 2025
5. Addressing other potential issues:

• Fuel Pump: Check the fuel pump and fuel filter for proper operation. 
• Fuel Pressure Regulator: Ensure the fuel pressure regulator is functioning correctly. 
• Sensors: Inspect sensors like the MAF sensor, TPS sensor, and camshaft/crankshaft position sensors for any issues. 
• ECM/PCM: In some cases, the Engine Control Module (ECM) or Powertrain Control Module (PCM) may be faulty and require replacement. 

Important Note: If you are not comfortable performing these checks and repairs yourself, it is best to consult a qualified mechanic for assistance.