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P0307 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


This code means that cylinder number 7 in your car’s engine is misfiring. Each piston should have a specific amount of fuel at all times, and a misfire implies that it’s not getting the right amount. To ensure that your fuel combustion works appropriately, each cylinder needs to fire correctly. A wide array of problems can cause a misfire, and it’s one of the more severe codes you can discover. P0307 should be fixed as soon as possible.


To fully understand this code, you have to know how the pistons and the crankshaft work. Pistons are connected to the crankshaft, and each one has a spark plug on top. The plug controls the combustion of fuel within the cylinder. When all cylinders are firing correctly, the crankshaft spins evenly, and the car can run smoothly. When one or more cylinders are misfiring, it can damage both the piston and the crankshaft.

Specifically, the P0307 code detects an increase or decrease of the crankshaft’s rpm. When this change is greater than two percent, the code is triggered, and the check engine light comes on


Because there are so many elements that feed the fuel to the pistons, finding the source of this problem can be tricky. Here are some of the most common issues that may lead to a misfiring cylinder.

  • Faulty Spark Plug – the plug isn’t igniting the fuel at the right time
  • No Compression – for the fuel to ignite, the cylinder has to be compressed
  • Damaged or Worn Spark Plug Wires – if the wiring is faulty, the plug won’t work
  • Damaged or Worn Spark Plug Coils – this coil converts electrical energy into a spark
  • Damaged Distributor Cap – not all cars have this, but it’s the cap that holds the spark plug wires
  • Damaged Rotor Button – not all vehicles have this either. It’s the piece that directs voltage to the correct cylinder when firing.
  • Faulty Fuel Injector – this component feeds fuel into the engine to be combusted
  • Clogged Exhaust Gas Recirculation Valves – the EGR redirects some of your exhaust back into the fuel, so it burns cleaner. If this valve is clogged, the fuel can get dirty and not fire correctly.
  • Burnt Valves – over time, the heat from combustion can weaken the valve, causing it to fail
  • Inaccurate Ignition Timing – the timing sensor controls when each cylinder fires
  • Vacuum Leaks – leaks in the system can reduce compression and cause gas to escape
  • Low Fuel Pressure – gas may not be getting to the cylinder as evenly as it should
  • Head Gasket Leaks – the head gasket keeps the combustion system vacuum sealed
  • Faulty Catalytic Converter – this piece removes pollutants from the gas, so it burns better

Another potential reason for this code is that one of the numerous sensors within the system may be faulty. The sensors involved will include:

  • Camshaft Sensor
  • Crankshaft Sensor
  • Mass Air Flow (MAF) Sensor
  • Oxygen Sensor
  • Throttle Position Sensor

Also, the powertrain control module (PCM) that controls how codes are detected may be faulty as well, leading to an inaccurate reading.


If you notice any of these problems with your vehicle, it could be a sign that you’re having trouble with a cylinder misfiring. You will want to check to make sure which cylinder is having the issue so you can pinpoint the cause.

  • The check engine light is on and/or flashing. If the light is flashing, that means the problem is severe.
  • You have difficulty starting the car, or it won’t start at all.
  • The vehicle stalls during acceleration, or at random times. It may also stall or die altogether when you’re stopped.
  • The engine sounds rough when you’re driving, and when you’re idling.
  • You notice a lack of power when driving (sluggish acceleration).
  • Your fuel consumption is much higher than average.

In rare cases, your car may not show any symptoms at all. If that is the case, though, it’s likely a faulty sensor or reading. Cylinder misfirings can affect the vehicle’s performance substantially, so you should notice something when driving.


Because there can be so many causes for this problem, you must follow these instructions step by step. Overall, it’s a process of elimination until you find the one component that is the culprit.

First, you want to check to see all of the codes stored in your PCM by using an OBDII scanner. Then, reset the system and start driving again. If the code comes back, you will have to find the source. If it doesn’t show, then it could be a faulty reading.

Next, you want to inspect your spark plugs. Pay close attention to the wiring, as well as the plug itself. Any damage or corrosion can be causing a misfire. Also, be sure to inspect the coil packs and coils themselves for any cracks or other damage.

If the spark plugs look good, then move onto the distributor cap and rotor button (if applicable). Again, look for any damage that could be causing a misfire.

If any of these parts look worn or damaged, you will want to replace them ASAP. If they are clean and intact, then you’ll have to move onto the fuel injection system. Pay attention to the wiring around the injector as well as the component itself.

In some cases, P0307 will be a result of another PCM code. If any other readings require repair, take care of those first. Afterward, reset the codes and do another test drive. If P03037 comes up again, then you’ll have to inspect the compression system for cylinder seven.

Common mistakes

Usually, the biggest mistake that people make when trying to repair the ignition system is to assume that a specific piece is working. Go through and inspect all potential problem areas, from the spark plugs to the fuel injector. Leave no component undisturbed.

How serious is this?

This code is one of the more severe you can encounter. A misfiring cylinder can cause the car to stall out or not turn on at all. Driving with a faulty cylinder can also damage the crankshaft and the engine. You cannot afford to wait on this issue.

What repairs can fix the code?

As you go through and inspect each piece, make a note of anything that has to be replaced. In most cases, you may have to replace one of the following components:

  • Spark Plugs
  • Spark Plug Wires
  • Ignition Coils and Coil Wires
  • EGR Valves and Tubes
  • Burnt Valves
  • Head Gasket
  • Camshaft Sensor
  • Crankshaft Sensor
  • MAF Sensor
  • O2 Sensor
  • Throttle Position Sensor
  • Fuel Injector and Wiring
  • Catalytic Converter

If there is damage to the cylinder itself, then you will have to replace the engine altogether. This is another reason to take action immediately. It’s a lot cheaper to replace a spark plug or some wiring than to get a whole new engine.

Related codes

P0300 codes are all related to cylinders. The number at the end of the code refers to the cylinder that’s having problems. They start with P0301 and go up to eight, depending on the type of vehicle you have.


If you detect this code, be sure to fix it immediately. If you do a full inspection and nothing seems to be broken, take your car to a professional. It’s not worth it to damage your engine and have to worry about costly repairs.

P0307 Code – What Does It Mean & How To Fix It