Symptoms of P0307
- Rough idle or a distinct shake, often worse at low RPM.
- A stumble or dead spot traced to cylinder 7.
- A flashing check-engine light when the misfire is active.
- Slight power loss and worse fuel economy.
Common causes of P0307
- A worn spark plug or failed ignition coil on cylinder 7.
- A clogged, leaking, or dead injector on cylinder 7.
- A vacuum leak or low compression local to that cylinder.
- Carbon-tracked plug boot or damaged coil wiring.
Useful checks before replacing parts
- Check whether cylinder 7 misfires at idle, under load, during cold start, or all the time.
- Inspect ignition output, injector control, injector flow, compression, vacuum leaks, and harness condition at cylinder 7.
- Use swap tests carefully and confirm whether the fault follows the part, stays with the cylinder, or changes with load.
How serious is P0307, and can you keep driving?
- Urgency
- High when the lamp is flashing
- Safe to drive?
- A flashing check-engine light means stop — a steady one means drive gently and get it looked at.
This is the one code family where the lamp itself tells you the urgency. A steady light means the misfire was detected and logged. A flashing light means it is happening right now and is severe enough to be dumping raw fuel into the catalytic converter, which can overheat and be destroyed in minutes rather than months. Pull over, switch off, and get the car recovered rather than driving it on. A converter costs many times what a coil or a plug does.
Clearing P0307, and making it stay gone
Clearing P0307 with a scan tool switches the lamp off; it does not fix anything, and it throws away the freeze-frame snapshot the car saved when the fault set. That snapshot is the most useful diagnostic evidence you have, because it records the load, RPM and temperature at the moment the test failed. Read it before you erase it.
Left alone, the lamp goes out on its own once the monitor that failed runs and passes on three consecutive driving cycles. The code stays in history after that, which is how a workshop can still see it. Disconnecting the battery is not a shortcut — it clears the stored codes and every learned fuel-trim value with them, so the car relearns from scratch and the underlying fault simply sets the code again.
On vehicles from roughly 2010 onward there is also a permanent DTC, which no scan tool can erase at all. It clears only when the monitor genuinely passes. That is deliberate: it stops a code being wiped in the car park outside an emissions test.
What P0307 costs to put right
There is no honest single figure for P0307, and any page that gives you one is guessing. The code names a circuit or a failed monitor, not a part — the same code can be a chafed wire, a connector full of water, or the component itself, and those are three very different bills.
The number worth budgeting for is diagnostic time. An hour of it is almost always cheaper than the second part you buy after the first one does not fix it, and parts fitted on a guess are rarely refundable once installed. If you are getting a quote, ask what the diagnosis found rather than what is being replaced — a ignition / misfire fault traced to a specific cause is a repair, and a list of parts is a hopeful shopping list.
Questions people ask about P0307
What does P0307 mean?
P0307 indicates a detected misfire on cylinder 7. It is a cylinder-specific lead, not a direct instruction to replace ignition parts.
Can I drive with P0307?
A flashing check-engine light means stop — a steady one means drive gently and get it looked at. This is the one code family where the lamp itself tells you the urgency. A steady light means the misfire was detected and logged. A flashing light means it is happening right now and is severe enough to be dumping raw fuel into the catalytic converter, which can overheat and be destroyed in minutes rather than months. Pull over, switch off, and get the car recovered rather than driving it on. A converter costs many times what a coil or a plug does.
What causes P0307?
The usual candidates are a worn spark plug or failed ignition coil on cylinder 7; a clogged, leaking, or dead injector on cylinder 7; a vacuum leak or low compression local to that cylinder; carbon-tracked plug boot or damaged coil wiring. The code tells you which test failed, not which of those did it — that is what the checks on this page are for.
Will P0307 clear itself?
Left alone, the lamp goes out on its own once the monitor that failed runs and passes on three consecutive driving cycles. The code stays in history after that, which is how a workshop can still see it. Disconnecting the battery is not a shortcut — it clears the stored codes and every learned fuel-trim value with them, so the car relearns from scratch and the underlying fault simply sets the code again.
Does P0307 mean I need to replace a part?
Do not overlook mechanical causes such as compression loss or valve sealing when ignition and injector checks pass.
How much does it cost to fix P0307?
There is no honest single figure for P0307, and any page that gives you one is guessing. The code names a circuit or a failed monitor, not a part — the same code can be a chafed wire, a connector full of water, or the component itself, and those are three very different bills.
Related OBD-II codes
These nearby ignition / misfire entries can help compare wording and pin down the fault area.