Fuel Delivery
P0306
Cylinder 6 Misfire Detected
P0306 indicates the PCM detected repeated combustion failures on cylinder 6. The code identifies the affected cylinder, but testing is required to determine whether the fault is ignition, fuel, wiring, or mechanical.
Diagnostic Snapshot
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Learn the System
Before diagnosing this code, it helps to understand the system behind it.
Read Understanding Fuel Delivery SystemsTechnical Summary
P0306 indicates the PCM detected repeated combustion failures on cylinder 6. The code identifies the affected cylinder, but testing is required to determine whether the fault is ignition, fuel, wiring, or mechanical.
Final QA emphasis: P0306 requires correlation of cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence. The code should be diagnosed by reproducing the enable condition, proving loaded electrical integrity, and independently confirming the physical system. OEM thresholds and system design take priority over universal values.
What You'll Learn
- • Diagnose a cylinder 6 misfire logically
- • Use coil and injector swap tests correctly
- • Interpret freeze-frame and Mode $06 data
- • Know when compression testing is required
- • Avoid unnecessary parts replacement
Think Like a Technician
Do not assume the ignition coil is faulty. If swapping the coil moves the misfire, the coil becomes the leading suspect. If the misfire stays on cylinder 6, continue with injector, wiring, compression, and mechanical testing.
For P0306, ask three questions in order: what did the controller command or observe, can the circuit carry and report that condition correctly, and did the physical system actually respond? Use cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence to identify which layer fails first.
What This Code Means
Cylinder 6 is not contributing normal engine power because combustion is inconsistent.
System Overview
Learn how fuel, ignition and engine mechanical faults create cylinder-specific misfires.
Why This Code Sets
The PCM detects crankshaft speed changes that exceed the allowable misfire threshold for this cylinder.
Common Symptoms
- Check Engine Light
- Rough idle
- Hesitation
- Reduced power
- Poor fuel economy
- Flashing MIL under heavy load
Most Likely Causes
- 1. ignition fault on the affected cylinder
- 2. fuel injector delivery/control problem
- 3. compression, valve, piston/ring, or valvetrain fault
- 4. vacuum/intake leak affecting that runner or cylinder
- 5. coolant/oil intrusion or deposit-related combustion problem
- 6. PCM/driver or crank-signal interpretation fault after basic combustion causes are proven
Common Vehicles
- Ford
- GM
- Toyota
- Honda
- Nissan
- Ram
Freeze Frame Clues
Idle
Misfire only at idle often points toward ignition, injector balance, or compression.
Under Load
Misfire under load frequently indicates ignition breakdown.
Live Data Expectations
Review Mode $06 misfire counts, cylinder contribution, fuel trims, injector pulse width, and ignition timing before replacing parts.
Typical Verification Tests
- Scan tool review
- Coil swap
- Spark plug inspection
- Injector balance test
- Compression test
- Leakdown test
Before You Condemn
Verify spark, injector command, injector balance, compression, and wiring integrity before replacing major components.
Before Replacing Parts
Inspect the spark plug, verify coil output, confirm injector operation, and perform compression testing if needed.
Diagnostic Workflow
- Confirm P0306; save current, pending, history, freeze-frame, readiness, misfire/fuel-trim data where applicable, and the complete powertrain scan before clearing codes.
- Verify the exact definition — Cylinder 6 Misfire Detected — and review VIN-specific system design, enabling criteria, fail-safe strategy, wiring, component locations, bulletins, and test procedures.
- Prioritize companion DTCs and basic prerequisites: battery/charging voltage, module powers/grounds, engine mechanical condition, coolant temperature plausibility, and any shared reference or network faults.
- Recreate the freeze-frame condition safely and graph cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with RPM, load, temperature, vehicle speed, and system voltage.
- Inspect the relevant harnesses, connectors, hoses, pipes, grounds, vacuum lines, fuel/exhaust components, and recent repair areas before disconnecting or replacing anything.
- Compare commanded and actual data. Decide whether the failure is electrical, hydraulic/pneumatic, mechanical, combustion-related, or a sensor-plausibility problem before choosing the next test.
- Perform loaded electrical tests on affected powers, grounds, reference, signal, solenoid, injector, relay, or actuator circuits; static continuity alone is not sufficient for current-carrying circuits.
- Use bidirectional controls where supported to command the affected actuator or system and compare command with current/voltage feedback, sensor response, and actual physical operation.
- Independently verify the physical condition with the appropriate test: calibrated fuel-pressure equipment, smoke/EVAP test, compression/leak-down, ignition waveform, injector balance, airflow/pressure response, or another OEM-approved method.
- Separate bank-specific or cylinder-specific faults from shared-system faults by comparing the opposite bank, neighboring cylinders, redundant sensors, or common feeds under the same operating condition.
- Check for heat-, vibration-, and load-dependent failures by repeating the test as the system warms and by carefully manipulating suspect harness sections while monitoring data.
- Do not condemn a sensor because its reading is abnormal until an independent measurement establishes whether the sensor is wrong or accurately reporting a real physical fault.
- Do not condemn an actuator because it fails to respond until power, ground, control authority, mechanical freedom, and the load side of the circuit are proven.
- Before condemning the PCM, prove stable module powers/grounds, terminal tension, external loads, circuit capability, prerequisite inputs, network integrity, and current calibration/software.
- Repair only the fault supported by test evidence, then perform any required relearn, adaptation, fuel-trim reset, or monitor-specific service procedure.
- Repeat the original enable condition and verify P0306 remains absent current and pending, the monitored data is plausible, driveability is normal, and readiness progresses.
Labor & Inspection Checklist
- Freeze-frame
- Spark plug
- Ignition coil
- Injector
- Wiring
- Compression
- Road test
Shop Notes
A cylinder-specific code identifies the location of the misfire—not the failed component. Evidence from testing should drive the repair.
Final QA diagnostic boundary for P0306: Cylinder 6 Misfire Detected. The technician should center the diagnosis on cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence rather than treating the DTC as a replacement instruction.
Evidence hierarchy: preserve freeze-frame first; confirm prerequisites second; compare command/input with loaded circuit behavior third; verify the physical system independently fourth. This order prevents a biased PID or unloaded continuity test from driving the repair.
Failure-pattern note: separate faults that follow engine load, heat, vibration, bank, cylinder, key cycle, purge/EGR command, or pressure demand. A repeatable pattern is often more diagnostic than a single static reading.
Before-parts rule: sensors require plausibility proof, actuators require power/ground/control plus mechanical-response proof, and modules require external circuit/load proof. Do not use a code description as proof of component failure.
Safety/driveability note: Do not continue normal driving with an active severe misfire or flashing MIL. Unburned fuel can rapidly overheat the catalytic converter, and a mechanical misfire can worsen engine damage.
Verification standard: reproduce the original enable condition after repair, not merely a warm idle in the bay. Confirm the monitor's related PIDs remain plausible and that no pending code returns.
P0306 QA case-pattern 1: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 2: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 3: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 4: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 5: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 6: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 7: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 8: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 9: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 10: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 11: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 12: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
P0306 QA case-pattern 13: Reproduce the original operating condition and compare cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.
Mechanic's Tip
A controlled swap test is one of the fastest ways to separate ignition faults from fuel or mechanical faults.
Common Mistakes
- Replacing coils without testing
- Ignoring compression
- Skipping freeze-frame review
Tools Used During Diagnosis
- Professional scan tool
- Spark tester
- Multimeter
- Compression tester
- Leakdown tester
Customer Explanation
Cylinder 6 is not firing correctly. The cause could be the ignition system, fuel injector, wiring, or an internal engine problem. Proper testing identifies the exact fault before parts are replaced.
Frequently Asked Questions
What does P0306 mean?
P0306 is Cylinder 6 Misfire Detected. The monitor is focused on cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence.
Does the code prove a part has failed?
No. It identifies a failed monitored relationship. Electrical integrity, physical system behavior, and sensor plausibility must be separated before parts are replaced.
Is it safe to drive with P0306?
Do not continue normal driving with an active severe misfire or flashing MIL. Unburned fuel can rapidly overheat the catalytic converter, and a mechanical misfire can worsen engine damage.
What should be checked first?
Save freeze-frame and the complete scan, verify the exact system design by VIN, then reproduce the failure while comparing commanded data with actual electrical and physical response.
What freeze-frame clues matter most?
RPM, load, vehicle speed, coolant temperature, system voltage, fuel trims, pressure/airflow data, command state, and companion DTCs show whether the failure occurs at idle, startup, cruise, acceleration, deceleration, or high load.
What live data is most useful?
Graph cylinder 6 misfire counters, ignition energy, injector command/delivery, compression/leakage, relative compression, fuel trim, crankshaft speed variation, and operating-condition dependence plus system voltage, RPM/load, temperature, and relevant redundant or opposite-bank/cylinder data. Look for the first relationship that breaks.
Can another system create this code?
Yes. Shared voltage, airflow, fuel delivery, exhaust, vacuum, mechanical, or combustion faults can make the named monitor fail even when the named component is functional.
Should I replace the most common part first?
No. Common-failure statistics are useful for prioritizing inspection, not for skipping tests. Expensive or invasive parts should have at least two consistent forms of evidence.
When is professional equipment justified?
Enhanced graphing data and bidirectional controls are strongly recommended. Depending on the code, a pressure transducer/gauge, scope, current clamp, smoke machine, injector balance equipment, or compression/leak-down tools may be justified.
How do I verify the repair?
Repeat the original operating condition, confirm electrical and physical results agree, check current and pending codes, and complete enough of the drive cycle to show stable data and readiness progress.
Related Atlas Resources
Related Atlas Resources
Understanding Fuel Delivery Systems
Related Reference Chapters
Diagnostic Confidence
High
Related Codes
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