The P0306 OBD-II trouble code means the engine control module has detected a misfire associated with Cylinder 6.
Unlike P0300, which indicates random or multiple-cylinder misfires, P0306 identifies one specific cylinder. That gives you a smaller diagnostic target, but it does not prove the Cylinder 6 ignition coil has failed.
A worn spark plug, weak ignition coil, faulty injector, damaged circuit, intake leak, low compression, valvetrain failure, or cylinder-deactivation problem can all trigger P0306.
The computer knows Cylinder 6 is not contributing the expected power. It does not know which part should be replaced—and neither does the guy at the parts counter without testing it.
P0306 belongs to the misfire-code family covered in the complete Pro Street P-code OBD-II guide.
P0306 Quick Answer
| Item | Information |
|---|---|
| Trouble code | P0306 |
| Definition | Cylinder 6 Misfire Detected |
| System | Ignition and combustion |
| Severity | High |
| Safe to drive? | Only briefly if the misfire is mild and the Check Engine Light is not flashing |
| Most common causes | Spark plug, ignition coil, injector, wiring, intake leak, or low compression |
| Common symptoms | Rough idle, shaking, hesitation, power loss, and flashing Check Engine Light |
| Typical repair range | Approximately $30 to $6,000+, depending on the cause |
What Does the P0306 Code Mean?
P0306 breaks down as follows:
- P: Powertrain
- 0: Generic OBD-II code
- 3: Ignition or combustion misfire
- 06: Cylinder 6
The engine control module monitors small changes in crankshaft speed during each combustion event. A healthy cylinder accelerates the crankshaft slightly when the air-fuel mixture burns and pushes the piston downward.
When Cylinder 6 repeatedly contributes less power than expected, the crankshaft briefly slows. The computer recognizes that pattern, stores P0306, and may illuminate or flash the Check Engine Light.
P0306 identifies the cylinder associated with the misfire. It does not identify whether the failure involves spark, fuel, air, compression, valve timing, or an electrical circuit.
For a broader explanation of misfire behavior, visit our engine misfire symptoms, causes, and diagnosis guide.
Where Is Cylinder 6 Located?
Cylinder 6 location depends on the engine design and manufacturer’s numbering system.
P0306 commonly appears on:
- V6 engines
- Inline-six engines
- Flat-six engines
- V8 engines
- V10 engines
- V12 engines
On an inline-six engine, Cylinder 6 is normally positioned at one end of the cylinder head, but numbering direction must still be verified.
On a V6 or V8, Cylinder 6 may be located on either cylinder bank. Some manufacturers place odd-numbered cylinders on one bank and even-numbered cylinders on the other. Others number cylinders sequentially along each bank.
Never assume Cylinder 6 is the sixth ignition coil you happen to find.
Before disconnecting anything, verify the cylinder layout using:
- Factory service information
- Manufacturer repair manual
- Underhood emissions label
- Vehicle-specific firing-order diagram
- Reliable engine identification information
Testing the wrong cylinder wastes time and can create an entirely new misfire if the wrong connector, plug wire, or coil boot is damaged.
Common Symptoms of P0306
P0306 symptoms depend on how frequently Cylinder 6 misfires and the conditions under which the failure occurs.
Common symptoms include:
- Illuminated Check Engine Light
- Flashing Check Engine Light
- Rough idle
- Engine shaking or vibration
- Hesitation
- Poor acceleration
- Reduced engine power
- Hard starting
- Stalling
- Increased fuel consumption
- Raw fuel smell from the exhaust
- Failed emissions test
- Popping from the intake or exhaust
- Reduced turbo boost
- Limp mode
- Additional ignition or fuel-system codes
An intermittent P0306 may only appear during cold starts, idle, heavy acceleration, high engine load, or cylinder-deactivation operation.
A weak ignition coil may work normally at idle but fail under acceleration because higher cylinder pressure requires more ignition voltage.
How Serious Is P0306?
P0306 should be treated as a high-priority trouble code.
An active misfire can allow unburned fuel to enter the exhaust. That fuel may ignite inside the catalytic converter, causing it to overheat and fail.
Continued driving may also contribute to:
- Catalytic converter damage
- Oxygen sensor contamination
- Cylinder-wall fuel wash
- Engine oil dilution
- Burned exhaust valves
- Piston damage
- Excessive engine vibration
- Damaged engine or transmission mounts
- Reduced fuel economy
- Increased emissions
Stop Driving Immediately If:
- The Check Engine Light is flashing
- The engine shakes violently
- Power loss is severe
- The vehicle stalls
- A strong raw-fuel smell is present
- The engine overheats
- Mechanical knocking is heard
- Abnormal valvetrain noise develops
A flashing Check Engine Light generally indicates a catalyst-damaging misfire. Reduce engine load, pull over safely, and shut the engine off.
If the light remains steady and the engine runs reasonably smoothly, driving a short distance for diagnosis may be possible. Avoid heavy throttle, high RPM, towing, and boost.
Most Common Causes of P0306
Cylinder 6 can misfire because of ignition, fuel, airflow, electrical, compression, or valvetrain problems.
| Possible cause | Relative likelihood |
| Worn or fouled spark plug | Very high |
| Weak or failed ignition coil | Very high |
| Damaged coil boot or spark plug wire | High |
| Clogged or failed fuel injector | High |
| Coil or injector wiring fault | Medium |
| Intake manifold leak near Cylinder 6 | Medium |
| Low Cylinder 6 compression | Medium |
| Carbon buildup on an intake valve | Medium on direct-injected engines |
| Burned or leaking valve | Medium |
| Cylinder-deactivation lifter failure | Application dependent |
| Worn camshaft lobe | Application dependent |
| Damaged piston ring | Lower |
| Head gasket failure | Lower |
| Incorrect valve timing | Lower |
| PCM driver failure | Rare |
The best starting point depends on the vehicle, maintenance history, accompanying codes, and freeze-frame conditions.
P0306 and Cylinder-Deactivation Engines
P0306 deserves additional attention on engines equipped with cylinder deactivation.
Depending on the manufacturer, these systems may be called:
- Active Fuel Management
- Dynamic Fuel Management
- Multi-Displacement System
- Displacement on Demand
- Variable Cylinder Management
Some engines deactivate specific cylinders by controlling their intake and exhaust valves. If Cylinder 6 is one of the deactivated cylinders, a failed lifter, oil-control solenoid, restricted oil passage, wiring fault, or worn camshaft may cause a persistent P0306.
Clues pointing toward a cylinder-deactivation problem include:
- P0306 returns after the plug, coil, and injector test correctly
- Ticking or tapping noise
- Low compression on Cylinder 6
- Misfire begins after switching between cylinder modes
- Metal debris is found in the engine oil
- Valve lift is reduced on Cylinder 6
- Oil-pressure or cylinder-deactivation codes are also stored
Do not keep replacing ignition components when the rocker arm is barely moving. The spark plug cannot repair a camshaft, despite what the invoice may suggest.
Tools Needed to Diagnose P0306
Useful tools include:
- OBD-II scanner
- Scan tool with live misfire counters
- Digital multimeter
- Spark tester
- Spark plug socket
- Compression tester
- Cylinder leak-down tester
- Noid light
- Mechanic’s stethoscope
- Smoke machine
- Fuel-pressure gauge
- Borescope
- Vehicle-specific wiring diagram
- Factory service information
A basic scanner can retrieve P0306. A professional scan tool may also display Mode $06 results, individual-cylinder misfire counters, fuel trims, injector commands, cylinder-deactivation data, and freeze-frame information.
How to Diagnose P0306
Step 1: Confirm the Code
Connect the scan tool and record:
- Stored codes
- Pending codes
- Permanent codes
- Freeze-frame data
- Individual-cylinder misfire counts
Do not clear P0306 before saving the freeze-frame information.
Important data includes:
- Engine RPM
- Engine load
- Vehicle speed
- Coolant temperature
- Intake-air temperature
- Short-term fuel trim
- Long-term fuel trim
- Throttle position
- Fuel-system status
The conditions under which P0306 appeared provide valuable clues.
| When P0306 occurs | Possible diagnostic direction |
| Cold start | Leaking injector, deposits, coolant intrusion, or weak compression |
| Warm idle | Intake leak, injector imbalance, or mechanical problem |
| Heavy acceleration | Weak coil, worn plug, excessive plug gap, or low fuel delivery |
| Wet weather | Coil boot, plug wire, or connector insulation |
| During cylinder deactivation | Lifter, solenoid, oil-pressure, or camshaft problem |
| Constantly | Dead coil, failed injector, wiring fault, or low compression |
| After recent service | Loose connector, damaged wire, incorrect plug, or installation error |
Step 2: Check for Related Codes
P0306 may appear with other misfire, ignition, fuel, or valvetrain codes.
Related codes include:
- P0300 — Random or Multiple Cylinder Misfire
- P0301 — Cylinder 1 Misfire
- P0302 — Cylinder 2 Misfire
- P0304 — Cylinder 4 Misfire
- P0305 — Cylinder 5 Misfire
- P0307 — Cylinder 7 Misfire
- P0171 or P0174 — System Too Lean
- P0172 or P0175 — System Too Rich
- P0206 — Cylinder 6 Injector Circuit Malfunction
- P0356 — Ignition Coil F Primary/Secondary Circuit Malfunction
- Camshaft or crankshaft position codes
- Cylinder-deactivation or valve-control codes
Several cylinders misfiring together may indicate a shared problem such as:
- Low fuel pressure
- Contaminated fuel
- Large vacuum leak
- MAF sensor error
- Incorrect valve timing
- Weak charging-system voltage
- Poor engine ground
- Crankshaft position signal fault
Step 3: Verify Cylinder 6
Use reliable vehicle-specific information to identify Cylinder 6.
Inspect the surrounding area for:
- Disconnected coil or injector connectors
- Loose connector terminals
- Oil inside the spark plug well
- Coolant contamination
- Damaged wiring
- Rodent damage
- Cracked vacuum hoses
- Intake manifold leaks
- Harnesses touching hot components
- Loose engine grounds
If P0306 appeared immediately after service, begin with a careful visual inspection. A connector that was not fully seated can imitate an expensive failure with remarkable enthusiasm.
Step 4: Inspect the Cylinder 6 Spark Plug
Remove the Cylinder 6 spark plug and compare it with a plug from a healthy cylinder.
Check for:
- Worn electrodes
- Excessive gap
- Cracked porcelain
- Carbon fouling
- Oil contamination
- Wet fuel deposits
- Coolant deposits
- Overheating
- Incorrect heat range
- Incorrect plug type
- Improper installation
A fuel-wet plug may indicate that fuel is present but ignition is missing.
A dry plug may point toward insufficient fuel delivery.
Oil deposits may indicate worn rings, valve-guide problems, a leaking spark plug tube seal, or a PCV-related issue.
If the plugs have exceeded the manufacturer’s service interval, replace the complete set with the correct part number and gap.
Step 5: Swap the Cylinder 6 Ignition Coil
If the engine uses coil-on-plug ignition, move the Cylinder 6 coil to another cylinder.
For example, swap the Cylinder 6 and Cylinder 4 coils. Clear the codes and operate the engine under conditions similar to the original freeze-frame data.
If the code changes from:
P0306 to P0304
the ignition coil is likely defective.
If P0306 returns on Cylinder 6, the coil is probably not the cause.
Inspect the coil and boot for:
- Carbon tracking
- Cracks
- Oil contamination
- Moisture
- Corroded terminals
- Burned internal contacts
- Damaged insulation
Our ignition coil replacement guide explains how to inspect and replace coils without automatically replacing every coil on the engine.
Engines using a distributor, coil pack, or spark plug wires require different testing. Check plug-wire resistance, routing, insulation, and coil-pack output using factory procedures.
Step 6: Understand P0306 Versus P0356
P0306 and P0356 may appear together, but they describe different failures.
| Code | Meaning |
| P0306 | The PCM detected a combustion misfire associated with Cylinder 6 |
| P0356 | The PCM detected an electrical fault in Ignition Coil F’s primary or secondary circuit |
P0356 provides stronger evidence of a coil-circuit problem. Possible causes include:
- Failed ignition coil
- Missing coil power
- Damaged trigger circuit
- Loose connector
- Corroded terminal
- Wiring short
- Failed PCM coil driver
P0306 without P0356 means the misfire may still be caused by fuel, compression, airflow, or a mechanical problem.
Step 7: Test the Cylinder 6 Fuel Injector
A clogged, leaking, stuck, electrically open, or unpowered injector can trigger P0306.
Listen to the injector with a mechanic’s stethoscope and compare its clicking sound with the other injectors.
Further testing may include:
- Injector resistance test
- Injector voltage test
- Noid-light test
- Current-ramp test
- Injector balance test
- Fuel-pressure drop test
- Injector swap test where practical
Use manufacturer specifications for injector resistance and circuit testing.
Useful Pro Street injector references include:
- How to Test a Ford Ranger Fuel Injector
- How to Test Nissan Altima Fuel Injectors
- How to Test a Toyota Corolla Fuel Injector
- How to Test an Acura RSX Fuel Injector
Never loosen a gasoline direct-injection or diesel common-rail fuel connection without following the manufacturer’s pressure-relief procedure.
Step 8: Inspect the Coil and Injector Circuits
If the coil and injector test correctly, inspect their circuits.
Check for:
- Correct supply voltage
- Reliable ground
- Ignition-coil trigger signal
- Injector control pulse
- Loose terminal tension
- Corroded connector pins
- High circuit resistance
- Wiring shorted to voltage
- Wiring shorted to ground
- Harness damage
- Poor engine or PCM grounds
Use voltage-drop testing with the circuit operating whenever possible.
PCM failure is possible, but it is rare. Verify the component, wiring, voltage supply, grounds, and mechanical condition before replacing the control module.
Step 9: Check for an Intake Leak
An intake leak near the Cylinder 6 runner may create a localized lean condition.
Inspect:
- Intake manifold gasket
- Cylinder 6 injector seal
- Vacuum hoses
- PCV system
- Brake-booster hose
- Intake manifold
- Throttle-body gasket
A smoke test is generally the safest and most accurate way to locate an intake leak.
Strongly positive fuel trim at idle that improves when RPM increases frequently points toward a vacuum leak.
Step 10: Perform a Compression Test
If Cylinder 6 has spark, fuel, and correct electrical control, test its compression.
Compare Cylinder 6 with the other cylinders and use manufacturer specifications for minimum pressure and allowable variation.
Low compression may be caused by:
- Burned intake or exhaust valve
- Bent valve
- Worn piston rings
- Damaged piston
- Broken valve spring
- Collapsed lifter
- Failed cylinder-deactivation lifter
- Worn camshaft lobe
- Head gasket failure
- Cylinder-wall damage
- Incorrect valve timing
If Cylinder 6 compression is low, follow with a leak-down test.
Step 11: Perform a Leak-Down Test
Place Cylinder 6 at top dead center on its compression stroke and introduce regulated compressed air.
| Air heard or observed at | Likely fault |
| Throttle body or intake | Leaking intake valve |
| Exhaust outlet | Leaking exhaust valve |
| Oil filler opening | Piston rings or cylinder damage |
| Cooling system | Head gasket, cylinder head, or block damage |
| Adjacent cylinder | Head gasket failure between cylinders |
Leak-down testing is especially important when P0306 remains after the spark plug, coil, injector, and wiring have passed inspection.
Step 12: Inspect Valvetrain Operation
If the engine has low compression, valvetrain noise, or cylinder-deactivation hardware, inspect valve movement.
Depending on the engine, diagnosis may require:
- Removing the valve cover
- Comparing rocker-arm movement
- Measuring valve lift
- Inspecting pushrods
- Testing cylinder-deactivation solenoids
- Verifying engine oil pressure
- Inspecting the camshaft with a borescope
- Checking for metal in the oil filter
Reduced valve lift on Cylinder 6 may indicate a failed lifter or worn camshaft lobe.
Step 13: Check for Intake-Valve Carbon
Direct-injected engines may accumulate carbon on the intake valves because fuel no longer washes across the back of each valve.
Cylinder-specific deposits may cause:
- Cold-start P0306
- Rough idle
- Airflow imbalance
- Misfire that improves after warm-up
A borescope can help confirm deposits. Approved cleaning methods vary by manufacturer and may include media blasting or professional chemical cleaning.
Step 14: Clear P0306 and Verify the Repair
After repairing the verified fault:
- Clear stored and pending codes.
- Start the engine.
- Verify a stable idle.
- Monitor Cylinder 6 misfire counters.
- Recreate the original freeze-frame conditions when safe.
- Complete the manufacturer’s drive cycle.
- Scan for pending codes.
- Confirm that readiness monitors complete normally.
A repair is confirmed only when Cylinder 6 misfire counts remain normal and P0306 does not return.
Common P0306 Repairs and Costs
Prices depend on the vehicle, labor rate, accessibility, and actual failure.
| Repair | Approximate installed cost |
| Replace spark plugs | $50–$500 |
| Replace one ignition coil | $80–$450 |
| Replace plug wire or coil boot | $30–$250 |
| Clean or replace one injector | $150–$1,000 |
| Repair wiring or connector | $100–$700 |
| Repair intake or vacuum leak | $100–$900 |
| Intake-valve carbon cleaning | $400–$1,500 |
| Replace intake manifold gasket | $300–$1,500 |
| Replace failed lifter or camshaft | $1,500–$6,000+ |
| Cylinder-head or valve repair | $1,500–$5,000+ |
| Engine replacement | $4,000–$15,000+ |
Diagnose P0306 before requesting an estimate. The same code can represent an inexpensive spark plug or a failed camshaft.
Common P0306 Diagnostic Mistakes
Replacing the Coil Without Testing It
Swap the Cylinder 6 coil with another cylinder and see whether the misfire follows.
Confusing P0306 With P0356
P0306 indicates a combustion misfire. P0356 indicates an electrical malfunction involving the Ignition Coil F circuit. They are related but not interchangeable.
Testing the Wrong Cylinder
Always verify the firing order and cylinder layout, especially on V6 and V8 engines.
Ignoring the Spark Plug
A new coil will not repair a cracked, fouled, worn, or incorrectly gapped spark plug.
Replacing the Injector Without Testing It
Confirm injector power, control, resistance, and fuel delivery before replacement.
Ignoring Cylinder-Deactivation Hardware
On applicable engines, failed lifters, solenoids, oil passages, or camshaft lobes can cause a persistent Cylinder 6 misfire.
Skipping Compression Testing
If spark and fuel tests pass, check the engine mechanically instead of continuing to purchase ignition parts.
Replacing the Catalytic Converter First
The converter may be damaged because of the misfire. Repair P0306 before evaluating catalyst efficiency.
P0306 Frequently Asked Questions
Does P0306 Mean the Cylinder 6 Coil Is Bad?
No. A failed coil is common, but a spark plug, injector, wiring fault, vacuum leak, or mechanical problem can also trigger P0306.
Can P0356 Cause P0306?
Yes. P0356 identifies an electrical fault in the Ignition Coil F circuit, which commonly corresponds with Cylinder 6. Verify the manufacturer’s coil designation before testing.
Can a Bad Spark Plug Cause P0306?
Yes. A worn, cracked, fouled, or incorrectly gapped Cylinder 6 spark plug is one of the most common causes.
Can a Fuel Injector Cause P0306?
Yes. A clogged, leaking, stuck, electrically failed, or unpowered Cylinder 6 injector can produce a cylinder-specific misfire.
Can a Vacuum Leak Affect Only Cylinder 6?
Yes. An intake manifold gasket or injector-seal leak near the Cylinder 6 runner may create a localized lean condition.
Can a Bad Lifter Cause P0306?
Yes. A collapsed or failed lifter can prevent the Cylinder 6 valves from opening correctly. This is especially relevant on certain cylinder-deactivation engines.
Why Does P0306 Appear Only During Acceleration?
A weak coil, worn spark plug, excessive plug gap, or fuel-delivery problem may only fail when cylinder pressure and engine load increase.
Why Does P0306 Appear Only During a Cold Start?
Possible causes include a leaking injector, intake-valve deposits, coolant intrusion, low compression, or a temperature-sensitive electrical problem.
Can I Drive With P0306?
Only briefly if the engine runs reasonably smoothly and the Check Engine Light remains steady. Stop driving if the light flashes, the engine shakes severely, power drops, or raw fuel can be smelled.
Can P0306 Damage the Catalytic Converter?
Yes. Unburned fuel can overheat and destroy the catalytic converter.
Will P0306 Clear Itself?
The Check Engine Light may turn off after several successful drive cycles, but stored or permanent code data can remain until the required self-tests are completed.
Related Misfire and Ignition Codes
- P0300 — Random or Multiple Cylinder Misfire
- P0301 — Cylinder 1 Misfire
- P0302 — Cylinder 2 Misfire
- P0303 — Cylinder 3 Misfire
- P0304 — Cylinder 4 Misfire
- P0305 — Cylinder 5 Misfire
- P0306 — Cylinder 6 Misfire
- P0307 — Cylinder 7 Misfire
- P0308 — Cylinder 8 Misfire
- P0316 — Misfire Detected During Startup
- P0206 — Cylinder 6 Injector Circuit Malfunction
- P0356 — Ignition Coil F Primary/Secondary Circuit Malfunction
Explore the Pro Street OBD-II Code Libraries
Use the Pro Street cornerstone pages to find additional diagnostic trouble codes:
- All P OBD-II Codes Explained — Powertrain Codes
- All B OBD-II Codes Explained — Body and SRS Codes
- All C OBD-II Codes Explained — Chassis Codes
- OBD-II DTC Doctor
P0306 identifies a misfire associated with Cylinder 6. Start with the freeze-frame data, verify the correct cylinder, inspect the spark plug, and swap-test the coil.
If the misfire remains on Cylinder 6, test the injector and electrical circuits before checking compression, valve operation, and cylinder-deactivation hardware.
Testing may take longer than firing random parts at the engine, but it is considerably less embarrassing when the Check Engine Light stays off afterward.
