Defective ignition coil on cylinder 6. Worn or faulty spark plug, spark plug wire or boot, or distributor cap and rotor where fitted. Major vacuum leak. Fuel delivery problems: low or weak fuel pressure, fuel pump, fuel pump relay or clogged fuel filter. EGR problems, such as an EGR valve stuck wide open or clogged EGR ports. Incorrect ignition timing or a defective MAF, crankshaft, camshaft or throttle position sensor (listed by RepairPal). Mechanical engine problems such as low compression, a leaking head gasket or valve problems. Faulty fuel injector (listed by OBD-Codes.com; RepairPal calls injectors and oxygen sensors common misdiagnoses).

Replace the ignition coil, spark plug, plug wire or boot on cylinder 6 (OBD-Codes.com recommends replacing the plug and boot if the coil is replaced). Repair vacuum leaks. Repair fuel delivery problems or a faulty injector once testing confirms it. Repair a stuck EGR valve or clogged EGR ports. Repair ignition timing or sensor faults found during diagnosis. Repair mechanical problems found by a compression or leak-down test.

P0306⚡ Ignition / engine misfireStop and fix promptly

P0306: Cylinder 6 Misfire Detected (Meaning, Causes, Fixes)

Q: What does P0306 mean?

P0306 means the engine computer has detected that cylinder 6 isn't firing properly. OBD-Codes.com says it's most often an ignition problem (a coil, spark plug, plug wire or boot giving low or no spark), but fuel delivery problems, a large vacuum leak, EGR faults, sensor faults and mechanical engine problems can also set it. P0306 is a generic OBD-II code, so it applies to all OBD-II vehicles, though repair steps vary by make and model. RepairPal explains that the misfire monitor counts crankshaft sensor pulses, and when cylinder 6 isn't contributing its share (more than about a 2 percent RPM variance between cylinders) it sets P0306. OBD-Codes.com adds that if the misfire isn't consistent or severe enough, the code may show as pending and the check engine light may only flash while the misfire is actually happening; once it becomes more consistent the code is stored and the light stays on. Cylinder 6 only exists on engines with six or more cylinders (most often a V6 or inline-six), and cylinder numbering differs between engines, so check your service information to find it. The sources disagree on fuel injectors: OBD-Codes.com lists faulty fuel injectors as a possible cause, while RepairPal lists fuel injectors and oxygen sensors among the common misdiagnoses for P0306. OBD-Codes.com also names a stuck-open EGR valve, clogged EGR ports and fuel pump, relay or filter problems, while RepairPal adds incorrect ignition timing, low fuel pressure and MAF, crank/cam and throttle position sensor faults.

Q: Can I keep driving with P0306?

Stop and fix promptly. Both sources treat P0306 as serious. RepairPal rates it 'Urgent', meaning a malfunction that can cause severe damage to the vehicle, and OBD-Codes.com says it should be classified as severe because the conditions behind it are likely to damage the catalytic converter and/or the engine. If the check engine light is flashing, ease off, avoid hard acceleration and get it checked as soon as you safely can.

Reviewed 2026-10-22 · Based on 2 cited source(s)

What P0306 means

P0306 is a generic OBD-II code, so it applies to all OBD-II vehicles, though repair steps vary by make and model. RepairPal explains that the misfire monitor counts crankshaft sensor pulses, and when cylinder 6 isn't contributing its share (more than about a 2 percent RPM variance between cylinders) it sets P0306. OBD-Codes.com adds that if the misfire isn't consistent or severe enough, the code may show as pending and the check engine light may only flash while the misfire is actually happening; once it becomes more consistent the code is stored and the light stays on. Cylinder 6 only exists on engines with six or more cylinders (most often a V6 or inline-six), and cylinder numbering differs between engines, so check your service information to find it. The sources disagree on fuel injectors: OBD-Codes.com lists faulty fuel injectors as a possible cause, while RepairPal lists fuel injectors and oxygen sensors among the common misdiagnoses for P0306. OBD-Codes.com also names a stuck-open EGR valve, clogged EGR ports and fuel pump, relay or filter problems, while RepairPal adds incorrect ignition timing, low fuel pressure and MAF, crank/cam and throttle position sensor faults.

Severity: can I keep driving?

Stop and fix promptly

Both sources treat P0306 as serious. RepairPal rates it 'Urgent', meaning a malfunction that can cause severe damage to the vehicle, and OBD-Codes.com says it should be classified as severe because the conditions behind it are likely to damage the catalytic converter and/or the engine. If the check engine light is flashing, ease off, avoid hard acceleration and get it checked as soon as you safely can.

Common symptoms

Check engine light on, or flashing while the misfire is happening
Rough or unstable running, at idle or under light acceleration
Diminished engine performance or lack of power, especially when accelerating
Odd smell from the exhaust (listed by OBD-Codes.com)
Dying at stop signs, hesitation or lower fuel economy (listed by RepairPal)
Often no adverse symptoms noticed by the driver (noted by RepairPal)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Defective ignition coil on cylinder 6
Worn or faulty spark plug, spark plug wire or boot, or distributor cap and rotor where fitted
Major vacuum leak
Fuel delivery problems: low or weak fuel pressure, fuel pump, fuel pump relay or clogged fuel filter
EGR problems, such as an EGR valve stuck wide open or clogged EGR ports
Incorrect ignition timing or a defective MAF, crankshaft, camshaft or throttle position sensor (listed by RepairPal)
Mechanical engine problems such as low compression, a leaking head gasket or valve problems
Faulty fuel injector (listed by OBD-Codes.com; RepairPal calls injectors and oxygen sensors common misdiagnoses)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Read all stored codes and freeze frame data and write them down. Note the RPM, load and speed when the code set, since that tells you when the misfire happens.
If lean, fuel supply or EGR codes are also stored, OBD-Codes.com says to diagnose and fix those first, because they can cause the misfire.
With the engine off and cool, inspect the cylinder 6 coil, spark plug and boot. OBD-Codes.com says parts contaminated with oil, coolant or water must be cleaned or replaced.
Check the wiring and connector to the cylinder 6 ignition coil and repair any damage.
If the spark plugs are due by your maintenance schedule, replacing them now is a sensible first step.
With the engine running, listen for a large vacuum leak (a hiss) around the intake.
If the coil and plug are easy to reach, swap them with another cylinder, clear the codes and see whether the misfire moves to that cylinder (RepairPal suggests swapping parts when your scan tool has no per-cylinder misfire counter).

Typical fixes

Replace the ignition coil, spark plug, plug wire or boot on cylinder 6 (OBD-Codes.com recommends replacing the plug and boot if the coil is replaced)
Repair vacuum leaks
Repair fuel delivery problems or a faulty injector once testing confirms it
Repair a stuck EGR valve or clogged EGR ports
Repair ignition timing or sensor faults found during diagnosis
Repair mechanical problems found by a compression or leak-down test

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

The check engine light is flashing
The misfire stays on cylinder 6 after replacing the plug and coil
Cylinder 6 is hard to reach, for example under the intake manifold on the rear bank of some V6 engines
A compression or leak-down test is needed to check valves, rings or the head gasket
Testing spark with the engine running under load: OBD-Codes.com describes a procedure that needs an assistant and the vehicle in gear, which is risky to do at home

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with P0306?

Both sources treat it as serious: RepairPal rates it 'Urgent' and OBD-Codes.com calls it severe. A misfire can damage the catalytic converter, so limit driving, especially if the check engine light is flashing, and get it fixed soon.

Is P0306 always a bad coil or spark plug?

No. OBD-Codes.com says ignition defects are the most common cause, but vacuum leaks, fuel delivery, EGR faults, sensors and mechanical problems like low compression can also cause it. Swapping the coil or plug to another cylinder is a cheap way to see if the misfire follows the part.

What's the difference between P0300 and P0306?

P0306 pins the misfire to cylinder 6. P0300 means random or multiple cylinders are misfiring, which usually points to something shared by all cylinders, such as fuel pressure or a vacuum leak.

Sources

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.