P0307 — Cylinder 7 Misfire Detected

OBD2 code P0307 flags a problem with the engine misfire monitoring (cylinder 7 misfire detected). Short, gentle driving to a shop is usually possible. Common culprits: clogged or leaking fuel injector, faulty crankshaft/camshaft position signal, failed ignition coil or coil wiring.

powertrain (engine/transmission)

Is it safe to drive?

Repair promptly P0307 should be diagnosed before extended driving because a continuously misfiring cylinder 7 can overheat the catalytic converter. If the check-engine light is flashing, the engine is shaking severely, or power drops sharply, stop driving and arrange repair.

Typical symptoms

P0307 stored in the powertrain control module, often with the check-engine light illuminated
A rough, uneven idle or hesitation during light acceleration
A noticeable stumble or loss of power when the engine is under load
Engine vibration that becomes more pronounced as cylinder 7 combustion becomes irregular
Increased fuel consumption or a noticeable change in engine responsiveness
In severe cases, an exhaust pop or combustion odor from unburned fuel

Common causes

A failed ignition coil, spark plug, or high-tension wire preventing cylinder 7 from producing a normal spark
A clogged, leaking, or electrically faulty fuel injector on cylinder 7
Low compression in cylinder 7 caused by worn piston rings, damaged valves, or a damaged cylinder head
Carbon buildup, a cracked ceramic spark plug, or a damaged ignition connector specific to cylinder 7
An ignition-control circuit or connector fault that intermittently suppresses the cylinder 7 spark
A vacuum leak severe enough to leave unburned fuel in the cylinder 7 combustion chamber

How to diagnose with an OBD scanner

Read P0307 with an OBD scanner Connect an OBD scanner using an ELM327 adapter or use AIScanAuto to read stored, pending, and permanent codes. Capture the P0307 freeze-frame data, operating conditions, and any cylinder-specific misfire counters before clearing anything.
Confirm the cylinder 7 location Use the engine's cylinder numbering and firing order to identify cylinder 7 correctly. If the scanner supports a cylinder contribution test, compare cylinder 7 with the other cylinders; do not diagnose the wrong bank or cylinder.
Test the cylinder 7 ignition system Inspect the cylinder 7 spark plug, coil, connectors, and any applicable ignition wires for cracks, carbon fouling, corrosion, or heat damage. Perform a spark test and verify that the ignition control system is commanding cylinder 7 correctly.
Check fuel delivery to cylinder 7 Inspect the cylinder 7 injector connector and wiring, check fuel pressure, and command the injector with a scan tool if supported. A good command signal with poor injector flow still points to a restricted or leaking cylinder 7 injector.
Verify compression and confirm the repair Perform a compression or leak-down test if ignition and fuel checks do not explain P0307. After repairing the confirmed fault, clear the code with the scanner and road-test while monitoring for P0307 and the return of the cylinder 7 misfire counter.

Approximate repair cost

Typical independent-shop estimates are about $100-$250 for diagnosis and $200-$1,500 for common ignition, plug, or injector repairs. Internal valve or compression repairs can cost more. These figures are estimates and vary by region, vehicle configuration, and the failed part.

Common questions

Is P0307 the same as a general engine misfire code?

No. P0307 specifically identifies a detected misfire in cylinder 7, so diagnosis should focus on that cylinder's spark, fuel delivery, and compression rather than treating it as an unspecified engine fault.

Can I safely keep driving with P0307?

Only cautiously for a short distance if the engine runs smoothly and the check-engine light is not flashing. A flashing light, severe shake, or major power loss warrants stopping because continued operation can damage the catalytic converter.

What are the most common causes of P0307?

Common causes include a bad cylinder 7 coil or spark plug, a clogged or leaking cylinder 7 injector, damaged ignition wiring, and low compression caused by valves, rings, or head damage.

Will clearing the P0307 code fix the misfire?

No. Clearing P0307 only erases the stored information; the fault will normally return if the cylinder 7 ignition, fuel, or compression problem remains. Repair the confirmed cause and then verify the code stays clear.

When your engine control module decides something is wrong with cylinder 7, it logs trouble code P0307. Think of it as the car's way of telling you one cylinder isn't pulling its weight during the combustion cycle. The powertrain control module constantly monitors the rhythm of each cylinder through the crankshaft position sensor, and when one cylinder misfires consistently, P0307 gets triggered. This isn't a random sensor glitch — the module waits for a repeatable pattern under specific load and RPM conditions before illuminating that dashboard warning light.

On most inline engines, cylinder 7 sits toward the front of the block near the accessory belt end. On V-type engines, the numbering varies by manufacturer, so you'll want to find your specific vehicle's firing order diagram before poking around. The location matters because some cylinders sit buried under the intake manifold, which adds hours to any repair job. The freeze frame data stored alongside P0307 is your roadmap — it captures engine load, RPM, coolant temperature, and vehicle speed the exact moment the misfire was detected. Recreating those conditions during diagnosis makes the problem far easier to catch.

Symptoms

The Check Engine Light stays illuminated or flashes rapidly during acceleration
The engine shakes noticeably at idle, feeling rough and uneven
Fuel economy drops because unburned fuel passes through the engine
You notice a stronger than normal smell of raw gasoline from the exhaust
The vehicle hesitates, jerks, or stumbles when you press the accelerator
Performance feels weak, especially under load or when climbing hills

Causes

Worn, cracked, or fouled spark plugs that fail to ignite the air-fuel mixture properly
A vacuum leak somewhere in the intake manifold allowing unmetered air to enter
A weak or failing fuel injector serving cylinder 7
Faulty ignition coil pack or individual coil-on-plug unit
Incorrect fuel pressure from a failing fuel pump or clogged fuel filter
Low compression in cylinder 7 due to worn piston rings, failed head gasket, or burnt valve
Problems with the crankshaft or camshaft position sensors causing timing errors

How to Diagnose

Hook up an OBD2 scanner, confirm P0307 is active in the stored codes, and record the freeze frame data — this snapshot reveals the exact conditions when the misfire first appeared.
Pull all related diagnostic trouble codes. A P0171 or P0174 (lean condition) alongside P0307 points toward a vacuum leak, while a fuel pressure code might indicate a weak pump.
Inspect the wiring harness and connectors at cylinder 7's ignition coil and fuel injector. Look for damaged insulation, corrosion buildup, or loose connections that could interrupt the signal.
Examine the spark plug for cylinder 7 — black soot suggests a rich mixture, a wet plug points to fuel flooding, and a white blistered appearance indicates a heat problem.
Swap the ignition coil from cylinder 7 with another cylinder's coil, clear the codes, and road test. If the misfire code moves to a different cylinder, you've found your bad coil.
With the engine cold, perform a compression test on cylinder 7 and compare the reading to the other cylinders. More than 15% difference between the lowest and highest readings indicates internal engine damage.

Repair Options with Costs

The right fix depends entirely on what's actually broken. Most P0307 diagnoses end up being straightforward parts failures:

Replace spark plugs ($90–$250): Plugs are the most common culprit and the cheapest fix. Always replace them in sets even if only one cylinder is flagged.
Replace ignition coil ($150–$380): Individual coil-on-plug units fail regularly, especially in high-mileage engines. Labor is minimal since the coil sits on top of the spark plug.
Clean or replace fuel injector ($200–$600): Clogged injectors starve a cylinder of fuel. 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