What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to vehicles equipped with OBD-II. Although generic, specific repair steps may vary by make/model.
A P0307 code means the car’s computer has detected that one of the engine’s cylinders is misfiring. In this case, it’s cylinder #7.
Symptoms
Symptoms may include:
Engine may be harder to start
Engine may stumble/stutter and/or hesitate
Other symptoms may also be present
Causes
A P0307 code could mean one or more of the following has occurred:
Faulty spark plug or wire
Faulty ignition coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Fuel shortage
Poor compression
Faulty computer
Possible Solutions
If there are no symptoms, the simplest thing to do is reset the code and see if it returns.
If there are symptoms such as the engine stumbling or hesitating, check all wiring and connectors leading to the cylinders (e.g., spark plugs). Depending on how long the ignition components have been in service, it may be a good idea to replace them as part of your regular maintenance schedule. I recommend spark plugs, spark plug wires, distributor cap and rotor (if applicable). Otherwise, check the ignition coils (e.g., coil packs). In some cases, the catalytic converter has failed. If you smell rotten eggs from the exhaust, your catalytic converter needs to be replaced. I’ve also heard in other cases that the issues were due to faulty fuel injectors.