Code P0300 Prius – Meaning, Causes & Fixes

Typically, a car’s engine will have anywhere from four to eight cylinders. More cylinders usually mean more power in your engine. As you start burning fuel, energy is generated in the engine’s cylinder, propelling your vehicle forward.

During combustion, the pistons rise and regularly fall, increasing the engine’s output. But if the ignition timing is off, a misfire will occur. The P0300 error code is displayed when two or more cylinders fail to fire properly.

Here’s What The P0300 DTC Means

“Random or Multiple Cylinder Misfire Detected” is the exact description of the P0300 DTC. The computer in your vehicle has picked up on a misfire in the engine that seems to be happening randomly and might affect one or more cylinders.

P0300 DTC Toyota Prius

The P0300 DTC will often be accompanied by another code ranging from P0301 to P0308. The second trouble code will specify which cylinder misfires, making the diagnosis much easier.

The afflicted cylinder is indicated by the last number in the above codes. For instance, a misfire on cylinder 2 would result in a P0302 code (in this example, cylinder 2). Inline four-cylinder engines are numbered from the end closest to the timing belt.

By recognizing the signs of this code, you can resolve the issue in time and prevent any further damage. One or more symptoms may be present, the most obvious being the P0300 code. If the misfire is really bad, a flashing check engine light will tell you that the misfire is severe enough to destroy the catalytic converter. Some drivers have reported the “triangle of death” also popping up on the instrument cluster.

Sometimes, there will be problems with the engine’s performance, such as a lack of acceleration and a noticeable delay in starting. You have to crank it over for a long time, and the vehicle still won’t start.

Your vehicle might be jerking as the engine stutters, resulting in poor fuel efficiency. A lack of power, a gasoline smell from the exhaust, and rough idling are also possible symptoms of a P0300 code. If you have to pass the emissions test, your car will fail if the engine is misfiring.

There are several potential causes for the P0300 error code, so consulting a mechanic is likely your best bet for finding out what’s wrong. The code suggests major problems and is one of those issues that should not be ignored. Therefore you should have your mechanic take a look at the vehicle immediately.

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What Could Cause A P0300 Code On Your Prius?

Engine misfires can be caused by faulty ignition, fuel, or an internal component. If your vehicle hasn’t been serviced recently, this is likely due to faulty or worn-out spark plug coil packs. Some of the causes of engine fault P0300 include the following.

  • Malfunctioning or broken spark plugs. 
  • Old or corroded ignition coils and wires.
  • Faulty fuel injectors. 
  • Mistiming of the ignition. 
  • Preventing the exhaust gas recirculation system from working properly due to a blockage in the EGR system. 
  • Loss of vacuum. 
  • Weak gasoline pressure. 
  • Cracked engine block seals. 
  • An imperfect distributor cap. 
  • Incorrect readings from the mass airflow sensor, camshaft, or crankshaft. 
  • Poor oxygen sensing due to a faulty sensor. 
  • Throttle position sensor failure.
  • The catalytic converter failed.
  • PCM is broken.
  • Distributor cap that is broken, old, or worn (only if applicable to the vehicle). 
  • The rotor button has been worn out or is broken (only if applicable to the vehicle). 

Insufficient ventilation of the exhaust system can cause the unburned gases to rekindle inside the catalytic converter, triggering the P0300 error message. A vehicle’s fuel economy can suffer if the catalytic converter is broken or blocked, and you will notice a considerable drop in your MPG.

In addition, a malfunctioning exhaust system will trigger the code P0300.

Misfiring, a lit check engine light, and fault codes P0300–P0312 can all result from a defective fuel pump that cannot supply the engine with sufficient fuel. If this occurs while the engine is operating, it could be because the air/fuel combination is lean, with too much air and insufficient fuel. Also, an air/fuel ratio sensor is a crucial input to your car’s computer, which regulates the fuel supply. A faulty sensor can cause engine misfiring and the dreaded error code P0300.

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How Can I Fix The P0300 DTC On My Car?

If you want to manually solve the P0300 error code, follow the instructions below. First, find out which cylinders aren’t firing properly to fix your car.

Swapping out a spark plug will usually fix this error code, hence I recommend doing this first.

Prius Bad Spark Plugs

You’ll need to take off the plug covers underneath the engine to get to the spark plug.

Check the distance between the spark plugs using a gapper (the range is 0.024 to 0.071 inches) and adjust it as needed.

If the spark plug is dirty or broken, clean it or replace it.

To change an ignition coil, you must unscrew it from the spark plug. Next, examine the ignition coil for any signs of corrosion or discoloration. The coil should be cleaned or replaced if it is dirty or broken. These could also fix the issue:

  • Spark plug wires and coils should be replaced if they are damaged.
  • When EGR tubes or valves get blocked, they must be fixed or replaced.
  • Fix any persistent holes or leaks.
  • Head gaskets should be replaced if they are leaking.
  • It would be best if you changed out the bad camshaft sensor, airflow sensor, oxygen sensor, and throttle position sensor.
  • Repairing or replacing catalytic converters and fuel injectors.
  • Remove the distributor cap and rotor button, and replace all of the wires, coils, and spark plugs (only if applicable to your car). 
  • Whenever possible, replace broken internal engine parts with new ones.
  • If there is cylinder damage, the engine should be replaced.
  • Get rid of that broken PCM and get a new one.

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Is The P0300 Code Serious?

Yes. The results of a P0300 code, which signals several misfires, can be disastrous. Codes P0301 through P0306 can indicate engine trouble, so be on the lookout. Misfiring cylinders can have a devastating effect on your vehicle’s handling and control.

In addition, if any P030X code is shown, your car may refuse to start and display codes P0300–P0304, or it may create dangerous driving circumstances. When a misfire occurs, you should get your car checked out right away by a professional mechanic.

Is It OK To Drive With A P0300 Code?

No. Avoid costly repairs to the catalytic converter and other internal engine parts by fixing the misfiring as soon as possible. In other words, if you read a P0300 error message, you should not operate the vehicle.

To determine the cause of error codes P0300, P0301, P0302, P0303, and P0304, it is best to take the vehicle to the nearest service center and have a technician take a look. A towing service can safely transport your vehicle to the garage of your choice if you experience any of the problems indicated by the engine light.

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How Much Does It Cost To Fix A P0300 Code?

This code, P0300, can be caused by several issues, including worn-out spark plugs, vacuum leaks, and insufficient engine compression. A precise price tag cannot be assigned until the issue is thoroughly analyzed.

When you bring your automobile in for a diagnosis, the shop will often charge you for an hour of “diag time,” or the time spent in labor determining the precise nature of the problem. You could pay anywhere from $75 to $150, depending on how much the shop charges per hour for labor. This diagnostic fee will be applied to the total price of repairs if you have the shop handle the work for you.

The problem, if properly identified, may need one or more of the following fixes. These estimates are based on average costs across the country and include materials and labor. Location and vehicle type will determine your final cost.

ItemEstimated cost 
Spark Plugs$66-$250
Spark Plugs Wires$180-$240
Fuel Injectors$1500-$1900
Ignition Coils$230-$640
Vacuum Leak$100-$200
Fuel Pump$1300-$1700
Fuel Pressure Regulator$200-$400
All Costs are estimates and will vary according to location

In Summary

A misfiring situation should not be treated lightly, as it can result in a hefty repair bill if not addressed on time. As soon as you notice your engine misfiring, it is time to drive the vehicle to a local repair shop and ask for a diagnosis.

More often than not, the issue is a bad spark plug, but if the vehicle has put some serious miles on it, the injectors of the fuel pump might need replacing.