P0307: Cylinder 7 Misfire Detected

What it means

Misfires concentrated on cylinder 7. A cylinder-specific code points away from shared causes (fuel pressure, MAF) toward components dedicated to that cylinder — coil, spark plug, injector, compression.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The engine control module estimates misfires by tracking changes in crankshaft speed as each cylinder fires. P0307 sets when those changes repeatedly indicate that cylinder 7 is not contributing normally; the cause may be its spark plug, ignition coil, injector, wiring, or compression.

Common causes

Most likely first.

1. Ignition coil failed
2. Spark plug worn or fouled

Symptoms

• Check engine light on or flashing
• Rough idle and uneven running
• Power loss, hesitation under acceleration
• Increased fuel consumption
• Possible smell of unburned fuel from exhaust

How to diagnose it

1. Check freeze-frame data and live misfire counts to see when cylinder 7 misfires and whether other cylinders are affected.
2. Inspect cylinder 7's spark plug, coil, and their connectors and wiring for wear, damage, oil, or moisture.
3. If the vehicle uses interchangeable coils or plugs, swap cylinder 7's part with another cylinder and see whether the misfire follows it.
4. Check cylinder 7's injector connector and wiring, then compare injector operation with the manufacturer's procedure.
5. If ignition and fuel checks do not identify the fault, compare cylinder 7 compression with the other cylinders.

Common fixes

• Replace a worn or fouled cylinder 7 spark plug.
• Repair a loose or damaged cylinder 7 ignition connector or wiring.
• Replace a failed cylinder 7 ignition coil if the fault follows it during a swap.
• Clean or replace a faulty cylinder 7 injector.
• Repair the cause of low compression in cylinder 7.

Can I keep driving?

If the check-engine light is flashing or the engine is shaking, stop driving as soon as it is safe; an active misfire can overheat and damage the catalytic converter. If the light is steady and the engine runs smoothly, keep driving to a minimum and avoid hard acceleration until diagnosed.