What P0307 means
Cylinder 7 isn't firing properly, so the engine runs rough, shakes at idle or hesitates. This code only shows up on engines with eight or more cylinders. The ignition coil or spark plug for cylinder 7 is the most common cause, sometimes just a loose coil connector or ground.
How the engine computer detects it
The engine module detects misfire from crankshaft speed: a cylinder that does not fire gives no acceleration impulse. At a catalyst-damaging rate (CARB: at least 5 % per 200 revolutions) the warning light flashes; at an emissions-relevant rate (at least 1 % per 1,000 revolutions – GM about 2–5 %, Ford 0.9–1.5 %) it comes on after two trips. Ford and GM may shut off a misfiring cylinder's injector to protect the catalyst. P0307 means more than 90 % of the detected misfires fall on cylinder 7. Usual causes are the ignition coil or spark plug of that cylinder, its injector, or low compression; a quick test is to swap coil or plug with a neighbouring cylinder and see whether the misfire moves. On V8 engines GM bulletins name loose coil connectors and a loose coil ground on the cylinder head.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on, flashing at a catalyst-damaging rate
- Rough idle, jerking, vibration
- Loss of power, hesitation
- Smell of unburnt fuel, higher consumption
Common causes
- Ignition coil of cylinder 7 faulty (coil, connector, ground) Most likely
- Spark plug of cylinder 7 worn, sooted, cracked or wrongly gapped Most likely
- Injector of cylinder 7 clogged or leaking, or its control Possible
- Low compression on cylinder 7 (valve, rings, head gasket) or local false air Less likely
- Water or oil in the plug well Less likely
How to diagnose P0307
- Find cylinder 7 on your engine. Numbering differs between manufacturers: some number one side 1–4 and the other 5–8, others alternate sides, so check the repair manual or the diagram on the intake.
- With the ignition off, make sure the coil connector on cylinder 7 is clipped in fully and that the coil's ground wire or mounting bolt is tight.
- Swap the cylinder 7 coil with one from another cylinder, clear the code and drive. If the misfire moves to that cylinder, replace the coil.
- Remove the cylinder 7 spark plug and check it for wear, cracks or oil, and the plug well for oil or water. If the plugs are due, replace the whole set.
- If the coil and plug are fine, have the cylinder 7 injector tested, then a compression test done. On engines that shut off cylinders to save fuel, a sticking valve lifter is also possible.
Vehicles that report P0307 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| GMC Sierra 1500 | 2015–2021 | 6 | — | |
| Chevrolet Silverado 1500 | 2014–2025 | 3 | — |
Counts of owner complaints to the NHTSA that mention P0307 (15 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 3
- Ignition system or misfire
- 07
- Specific fault
Questions drivers ask
Can I drive with code P0307?
If the check engine light is flashing, pull over and switch off: the misfire is bad enough to overheat the catalytic converter. With a steady light, drive gently and directly to a shop or home, and don't tow or haul heavy loads until it's fixed.
Will my car pass an emissions inspection with P0307?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0307 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0307 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.