P0306
Cylinder 6 Misfire DetectedP0306 is a generic OBD-II powertrain diagnostic trouble code: Cylinder 6 Misfire Detected. It is logged by the engine control unit when the misfire monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0306 means
P0306 is an OBD-II generic powertrain code meaning the engine control module (ECM) has detected a misfire on cylinder number 6. The ECM monitors crankshaft rotational velocity using the crankshaft position sensor; a misfire causes a detectable deceleration at the crank within each power stroke window, and when the dropout pattern points consistently to cylinder 6's firing event, P0306 is stored. The check engine light will illuminate and may flash rapidly if the misfire is severe enough to risk catalytic converter damage.
Cylinder 6 occupies different physical positions depending on engine layout. In a V6 it is typically the rearmost cylinder on Bank 2 (passenger side on most GM/Ford V6s); in an inline-6 it is the last cylinder in the bank; in a V8 (SAE firing-order convention) it sits on Bank 1; and in V10 or V12 configurations cylinder 6 is mid-bank. Because it is never the first cylinder in a firing order, P0306 is distinct from P0301–P0305 and should not be confused with P0303 (cylinder 3 misfire).
The root cause is almost always an ignition, fuel, or mechanical fault isolated to that cylinder: a worn spark plug, failed ignition coil, clogged or dead fuel injector, low compression from a leaking valve or worn rings, or a vacuum leak affecting only that intake runner. Less commonly, a wiring fault on the coil driver circuit or ECM driver failure can also cause a persistent cylinder-6-specific misfire count.
Common causes
Most-frequently reported root causes when P0306 is logged.
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1
Worn or fouled spark plug on cylinder 6 causing weak or absent spark.
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2
Failed or cracked ignition coil on cylinder 6 producing insufficient high-voltage output.
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3
Clogged or electrically dead fuel injector on cylinder 6 causing lean misfire.
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4
Low cylinder compression due to burnt exhaust valve, worn piston rings, or failed head gasket on cylinder 6.
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5
Vacuum leak at the intake manifold runner or gasket serving cylinder 6 creating an excessively lean mixture.
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6
Damaged or shorted wiring in the ignition coil driver circuit for cylinder 6.
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7
Faulty crankshaft or camshaft position sensor producing erroneous misfire attribution.
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8
ECM driver circuit failure preventing proper coil triggering on cylinder 6.
Symptoms drivers notice
How to diagnose P0306
A typical diagnostic flow when this code is present.
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1
Connect an OBD-II scan tool, confirm P0306, and check for companion codes such as P030X (other cylinders), P0300 (random misfire), or fuel/ignition system codes.
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2
Review freeze frame data for RPM, load, and coolant temperature at the time of the misfire to narrow operating conditions.
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3
Perform a coil and spark plug swap: move cylinder 6's coil and plug to a known-good cylinder and monitor live misfire counters — if the misfire count follows the parts, replace them.
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4
Test the cylinder 6 fuel injector for correct resistance (typically 12–16 Ω for high-impedance) and audible operation with a stethoscope; swap or bench-test if suspect.
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5
Perform a cylinder compression test and leak-down test on cylinder 6 to rule out mechanical causes (valve, ring, or head gasket failure).
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6
Inspect the ignition coil wiring harness connector and ground circuits at cylinder 6 for corrosion, chafing, or broken wires.
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7
If all external components test good, verify ECM coil driver circuit output with an oscilloscope before condemning the ECM.
Related powertrain codes
Frequently asked questions
Can I keep driving with a P0306 misfire?
Short-term driving to a workshop is possible, but sustained misfiring pumps raw fuel into the catalytic converter, which can destroy it within miles. If the check engine light is flashing, stop driving immediately.
Is P0306 the same as P0303?
No. P0303 indicates a misfire on cylinder 3; P0306 is specifically cylinder 6. They require separate diagnosis because cylinder 6 has its own spark plug, coil, and injector — swapping parts between the two cylinders is a common diagnostic step.
Will replacing the spark plug always fix a P0306?
Not always. While a worn spark plug is the most common cause, the misfire can also originate from a failed ignition coil, dead injector, low compression, or a vacuum leak. Perform a coil/plug swap test first to isolate whether the fault follows the component.
Which vehicles are most likely to show P0306?
Any multi-cylinder engine with six or more cylinders can produce P0306. It is common on V6, V8, V10, and V12 engines across all manufacturers. High-mileage vehicles with original ignition components are the most frequent candidates.
Disabling P0306 in software
RaceTune can permanently disable P0306 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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