Is P0307 ever caused by a bad crankshaft sensor?

Rarely on just one cylinder. A failing crank sensor usually causes random misfires on multiple cylinders (P0300). A single-cylinder code almost always points to that cylinder's own components.

Can spark plug wire problems cause P0307?

On older vehicles with spark plug wires. Most modern vehicles use coil-on-plug setups, where each coil sits directly on the plug with no wire.

The truck runs fine at highway speed but misfires at idle. Is that still urgent?

Yes. The misfire may be less severe at speed because load conditions change. But it is still damaging the converter and will likely worsen.

Codes › P0307

P0307: Cylinder 7 is misfiring

Cylinder 7 Misfire Detected

High severityCan you keep driving?

If the light is flashing, stop driving immediately. A flashing check engine light with a misfire means your catalytic converter is being damaged in real time. A steady light means drive directly to a shop.

What it means

P0307 only appears on V8, V10, or V12 engines. Cylinder 7 is typically on the driver-side bank toward the rear, which places it near the firewall on most rear-wheel-drive trucks and cars. The misfire itself is the same failure as any other single-cylinder code: incomplete combustion sends unburned fuel into the exhaust. What is different about cylinder 7 specifically is that on many V8 trucks, cylinder 7 shares a bank with cylinder 5 and access involves removing exhaust manifold heat shields or working around the transmission bellhousing.

Common causes

Failed ignition coil on cylinder 7Swap it with an adjacent coil to confirm before purchasing a replacement.
Worn spark plug on cylinder 7Rear bank plugs on V8 trucks often go longer between services due to difficult access.
Failed fuel injector on cylinder 7A balance rate test on a scan tool can confirm whether the injector is supplying correct fuel volume.
Compression loss on cylinder 7Burned valve or worn piston rings. A compression or leak-down test is required to confirm.

What it costs

Spark plug set$100 to $350 installed (higher on trucks with tight access)
Ignition coil (one)$150 to $450 installed
Fuel injector (one)$150 to $500 installed
Compression repair$1,200 to $4,000 depending on extent

Symptoms

Check engine light flashing or steady
V8 vibration at idle, noticeably uneven
Reduced power, especially noticeable in a truck under load
Fuel economy drop
Possible P0207 injector fault code alongside

What to do next

On most GM or Ford V8 trucks, cylinder 7 is at the rear of the driver bank. Confirm the cylinder location for your specific engine before reaching for tools. Coil swap first, plug inspection second. If a balance rate test is available on your scan tool, run it to check injector flow while you are diagnosing. A compression test should be part of the diagnosis if ignition and injection both test good.

Lewis shows cylinder 7 misfire counts, plus live fuel trim and ignition timing, so you have a complete picture of what the engine is doing around that cylinder. Download Lewis.

Related codes

FAQ

Is P0307 ever caused by a bad crankshaft sensor?: Rarely on just one cylinder. A failing crank sensor usually causes random misfires on multiple cylinders (P0300). A single-cylinder code almost always points to that cylinder's own components.
Can spark plug wire problems cause P0307?: On older vehicles with spark plug wires. Most modern vehicles use coil-on-plug setups, where each coil sits directly on the plug with no wire.
The truck runs fine at highway speed but misfires at idle. Is that still urgent?: Yes. The misfire may be less severe at speed because load conditions change. But it is still damaging the converter and will likely worsen.