# P0306: Cylinder 6 Misfire Detected **Verdict:** Drive to a shop this week Ignition and misfire - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $100-$1,500 - **Urgency:** This week - **Most likely:** Spark plug or ignition coil on cylinder 6 - **DIY?:** Steps 1-3 ## Quick answer P0306 means the engine computer has detected that cylinder 6 is not firing properly, so that cylinder is not making its share of power. The usual culprit is a worn spark plug or a failing ignition coil on cylinder 6, but a leaking fuel injector or low compression can also cause it. This code only appears on engines with six or more cylinders. ## What does P0306 mean? P0306 needs at least six cylinders. Cylinder 6 is the last cylinder on a V6 or inline six and one of the middle cylinders on a V8. On inline sixes, such as BMW and Toyota engines and the older Jeep 4.0, it is the rearmost cylinder, closest to the firewall. On Toyota and Honda transverse V6s it is on the front bank, the easier side to reach. Ford V6s put it at the rear of the driver's side, and GM and Chrysler V8s third on the passenger side. The computer tracks crankshaft speed through each firing event and assigns any slowdown to a cylinder using the firing order and the camshaft signal. P0306 means cylinder 6 is misfiring often enough to raise emissions, normally confirmed over two drive cycles, or badly enough to threaten the catalytic converter, which flashes the light right away. Because the code names one cylinder, start with parts that serve only cylinder 6. ## What are the symptoms of P0306? - Check engine light on, or flashing while you accelerate - Engine shakes or stumbles at idle - Loss of power or a jerky feel when you speed up - Worse fuel economy - Raw fuel or rotten-egg smell from the exhaust ## What causes P0306? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Worn or fouled spark plug in cylinder 6** (most common). Spark plugs wear gradually, their gap widening until the coil can no longer fire them reliably, and oil or carbon fouling speeds this up. On Toyota and Honda transverse V6s, cylinder 6 is on the front bank, so its plug is quick to check. If records show plugs past their interval, replace the full set before testing anything else. 2. **Failing ignition coil on cylinder 6** (common). Coils crack and break down with heat and age, and coil-on-plug designs fail one cylinder at a time. A failing cylinder 6 coil misfires under load first, then at idle. Swap it with a neighbor on the same bank, such as cylinder 5 on an inline six, clear the code and drive; if the code moves, replace the coil. 3. **Clogged or leaking fuel injector on cylinder 6** (less common). A dirty injector starves cylinder 6, causing a lean misfire mostly at idle, while a leaking one floods it and can cause a rough start after sitting. Direct-injection engines can suffer stuck injectors that wash oil off the cylinder wall. A shop runs an injector balance test, checks the electrical pulse or swaps injectors to see if the misfire moves. 4. **Vacuum leak near cylinder 6** (less common). A cracked intake gasket, loose vacuum line or split PCV hose near cylinder 6 adds air the mass airflow sensor never measured. That cylinder runs lean and misfires, mostly at idle or light cruise, sometimes with high fuel trims on its bank. Plastic intake manifolds and hoses harden with heat over the years. A smoke test reveals the leak. 5. **Low compression in cylinder 6** (rare). A burnt valve, worn rings, a collapsed lifter or a head gasket leak lowers cylinder 6 compression, so it misfires at every speed regardless of new ignition parts. Overheated or oil-burning engines are most at risk. A compression test shows a low reading, and a leak-down test shows whether air escapes past valves, rings or gasket. ## How do you diagnose P0306? 1. Read all stored codes and freeze-frame data to see the engine speed and load when the misfire happened. 2. Find which cylinder is number 6 on your engine (check a service manual, since the layout varies by make). 3. Pull the cylinder 6 spark plug and look for wear, oil, or heavy carbon. 4. Swap the cylinder 6 ignition coil with a neighbor, clear the code, and drive. If the code becomes that neighbor's number, replace the coil. 5. If plug and coil are fine, test the injector and run a compression test on cylinder 6. ## How do you fix P0306, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Replace spark plugs | $120-$450 | Plugs are usually replaced as a full set. Engines with rear plugs under the intake cost more in labor. | | Replace cylinder 6 ignition coil | $150-$400 | One coil, including labor, on most coil-on-plug engines. | | Replace cylinder 6 fuel injector | $250-$700 | Direct-injection engines sit at the top of this range. | | Repair low compression (valve or head gasket work) | $1,200-$3,500 | Only needed if a compression test confirms the problem. | Full price breakdowns: [spark plug replacement cost](/cost/spark-plug-replacement), [ignition coil replacement cost](/cost/ignition-coil-replacement). ## Is it safe to drive with P0306? > **Drive to a shop this week.** You can usually drive gently to a shop if the light is steady. If the check engine light is flashing, stop driving hard and get it fixed right away, because unburned fuel can overheat and ruin the catalytic converter. ## Will P0306 fail an emissions test? An OBD-based emissions test fails a car with P0306 and the check engine light on. Severe cylinder 6 misfires can also set catalyst codes for its bank later. Once repaired and cleared, the noncontinuous monitors, such as catalyst, oxygen sensor and EVAP, need several days of normal driving to report ready before the car can be retested. ## After the repair: clearing P0306 Clear the code and drive under the conditions shown in the freeze-frame data, such as idle or highway load, watching the cylinder 6 misfire counter if your scan tool shows it. On inline sixes, where cylinder 6 is nearest the firewall, recheck that its coil connector is fully latched, since rear connectors are easy to leave loose. ## How to prevent P0306 - Replace plugs as a full set on schedule, including the hard-to-reach rear cylinders. - Fix valve cover leaks promptly; on many inline sixes, oil leaks reach the plug wells. - Seat each coil connector until it clicks after any plug or coil work. - Replace a clogged PCV valve, which can push oil into the intake and foul plugs. - Use quality fuel and the octane grade your owner's manual specifies. ## Codes often seen with P0306 - [P0300](/codes/p0300): Random/Multiple Cylinder Misfire Detected - [P0301](/codes/p0301): Cylinder 1 Misfire Detected - [P0302](/codes/p0302): Cylinder 2 Misfire Detected - [P0303](/codes/p0303): Cylinder 3 Misfire Detected - [P0304](/codes/p0304): Cylinder 4 Misfire Detected - [P0305](/codes/p0305): Cylinder 5 Misfire Detected - [P0351](/codes/p0351): Ignition Coil "A" Primary/Secondary Circuit - [P0171](/codes/p0171): System Too Lean (Bank 1) ## Frequently asked questions ### Can I drive with a P0306 code? You can drive a short distance if the check engine light is steady and the engine runs reasonably smoothly. If the light is flashing, the misfire is severe enough to damage the catalytic converter, so ease off, avoid hard acceleration and get to a shop soon or arrange a tow. ### Where is cylinder 6? It depends on the engine, so check a service manual or diagram for your model. On inline sixes it is the rearmost cylinder, near the firewall. On Toyota and Honda transverse V6s it is on the front bank, while Ford V6s put it at the rear of the driver's side bank. ### Will new spark plugs fix P0306? They often do if the plugs are old, since worn plugs are the most common cause. Replace the full set, not just cylinder 6. If the code comes back after new plugs, swap the cylinder 6 coil with a neighboring cylinder to see whether the misfire follows the coil. ### How much does it cost to fix P0306? Most P0306 repairs cost $100 to $450 at an independent shop for plugs or a coil. Injector work runs $250 to $700, with direct-injection engines at the top of that range. Internal engine repairs for low compression, such as valve or head gasket work, can pass $1,500. ### Why do P0306 and P0300 show up together? P0300 with P0306 usually means cylinder 6 misfires most, but other cylinders are also missing now and then. Check cylinder 6 parts first, then shared causes such as worn plugs, a vacuum leak or low fuel pressure. Per-cylinder misfire counts on a scan tool show whether cylinder 6 is truly the main problem. ### Can a bad coil connector cause P0306? Yes, a loose, cracked or corroded connector on the cylinder 6 coil can interrupt the firing signal and cause misfires that come and go. Rear connectors on inline sixes are easy to leave unlatched after a plug job. Check that the connector clicks firmly and its pins are clean and dry. ### Can I fix P0306 myself? Often yes, if cylinder 6 is on an accessible bank or at the rear of an open inline-six engine bay. Replacing a coil or plug needs basic tools and a torque wrench. If reaching it means removing the intake plenum, or the cause is the injector or compression, a shop is the better choice. ### Is P0306 serious? It is moderately serious. A steady misfire costs power and fuel economy and slowly damages the catalytic converter, and a flashing light means damage can happen quickly. Most causes are inexpensive, but a misfire that does not follow the coil or plug may be a valve problem needing prompt diagnosis. ### Will P0306 pass inspection? No, an active P0306 with the check engine light on fails an OBD-based emissions inspection. After the repair, clear the code and drive normally for several days so the readiness monitors complete. A scan tool can confirm they are ready, which saves a wasted trip to the testing station. ### What should I check first for P0306? Check how old the spark plugs are first, since worn plugs are the most common cause. Then pull the cylinder 6 coil, look for oil or cracks, and do a coil swap test with a neighboring cylinder. If the misfire stays on cylinder 6, move on to the injector and a compression test. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other ignition and misfire codes - [P0300 Random/Multiple Cylinder Misfire Detected](https://diagxcar.com/codes/p0300) - [P0301 Cylinder 1 Misfire Detected](https://diagxcar.com/codes/p0301) - [P0302 Cylinder 2 Misfire Detected](https://diagxcar.com/codes/p0302) - [P0303 Cylinder 3 Misfire Detected](https://diagxcar.com/codes/p0303) - [P0304 Cylinder 4 Misfire Detected](https://diagxcar.com/codes/p0304) - [P0305 Cylinder 5 Misfire Detected](https://diagxcar.com/codes/p0305) - [P0307 Cylinder 7 Misfire Detected](https://diagxcar.com/codes/p0307) - [P0308 Cylinder 8 Misfire Detected](https://diagxcar.com/codes/p0308) - [P0316 Engine Misfire Detected on Startup (First 1000 Revolutions)](https://diagxcar.com/codes/p0316) - [P0320 Ignition/Distributor Engine Speed Input Circuit](https://diagxcar.com/codes/p0320) - [P0351 Ignition Coil "A" Primary/Secondary Circuit](https://diagxcar.com/codes/p0351) ## Symptoms - [Why is my car idling rough?](https://diagxcar.com/symptoms/rough-idle) - [Why does my car hesitate when I accelerate?](https://diagxcar.com/symptoms/car-hesitates-when-accelerating) ## Repair costs - [Spark plug replacement cost](https://diagxcar.com/cost/spark-plug-replacement): $120-$450 - [Ignition coil replacement cost](https://diagxcar.com/cost/ignition-coil-replacement): $150-$400 --- Source page: https://diagxcar.com/codes/p0306 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.