What is P0300 DTC? Common Symptoms, Causes, and Solution
For optimized engine performance, all engine cylinders must continuously fire the sparkplug. However, certain disorders in the firing can impact the RPM of your vehicle. If the percentage of RPM change due to misfiring cylinders is between 2-10%, then the DTC P0300 will occur.
P0300 is a severe-intensity DTC indicating that either one or more engine cylinders are misfiring, resulting in uneven RPM.
The common causes of P0300 include broken sparkplugs, crankshaft, gasket, low-quality fuel, and knocking and vacuum leaks.
The common symptoms of P0300 include check engine light, hard startup, lack of acceleration, and reduced fuel economy.
The solutions for this DTC include changing the sparkplugs, replacing the distributor cap, replacing the leakage components, and resetting the DTC.
The cost to resolve this issue can be as low as $20 (in case of crankshaft sensor failure) and as high as $2000 to replace the faulty fuel injectors.
Introduction
Modern vehicles have 4-6 cylinders; each cylinder fires a sparkplug to flame the air-fuel mixture. This results in effective combustion providing power to the crankshaft that must turn continuously while driving (2). For effective crankshaft movement, the cylinders must fire the sparkplugs continuously in a smooth manner. If one or more cylinders misfire, then there is a chance that the RPM (revolutions per minute) is increased or decreased (1). OBDII module generally analyses these problems and sends a DTC code to ECU. Hence, it turns on the warning light (4).
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So, if you are observing a check engine light along with fluctuation in the RPM of your vehicle, then there is a chance that the DTC is P0300. This is a severe intensity engine fault code illustrating that either one or more engine cylinder is misfiring.
This article will further analyze the causes, symptoms, and solutions of P0300 DTC.
How to Read P0300 DTC
The following table has read every character of P0300 DTC (2):
Number of Character
Specific Character
What does it Signify
First
P
The problem has to do with the powertrain part of the vehicle. Hence, the engine, transmission, or fuel system can malfunction.
Second
0
This means that the code is standardized, so the SAE manual can be used further to interpret the code instead of the instruction manual.
Third
3
This number illustrates the problem within the vehicle’s engine cylinders.
Fourth and Fifth
00
The specific fault index is 00, indicating that either one or more engine cylinder is misfiring, causing RPM fluctuations.
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P0300 means that this issue lies within the powertrain and is SAE standardized. Further, the DTC indicates that either one or more engine cylinder is misfiring, causing serious fluctuations in the vehicle’s RPM.
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Symptoms of P0300 DTC
Following are a few symptoms of P0300 DTC:
Check Engine Light
The first symptom of P0300 DTC is the check engine light. When the RPM fluctuates, the ECU will be sent an unreadable code by the OBDII module, and DTC P0300 will occur.
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Resultantly the check engine light will turn on. Modern vehicle makers have further added features in the warning lights, where warning lights start blinking on and off to illustrate the severity of the issue. When the percentage of increase or decrease in the RPM is between 2-10%, the check engine light will only come on. This illustrates that the issue is intermediate, and the driver should resolve it before damaging the engine components. On the other hand, if the percentage of RPM fluctuation exceeds 10%, then the misfiring cylinders can be greater, and the check engine light will blink on and off. This shows that the driver should stop driving and resolve the issue immediately.
Hard Startup
Another symptom of misfiring cylinders is a hard startup. When the cylinders are misfiring, the engine’s combustion process is disrupted, resulting in hard startups. This means that the driver will face difficulty in starting the engine.
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Further, the driver can notice the difference in the engine sound while starting. This is a sign that the engine is malfunctioning. In some cases, the engine may not start at all, and the driver has the push the car to start the car. In this case, the engine cylinder misfire impacts RPM percentage above 10% (5).
Lack of Acceleration
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Misfiring cylinders can also result in a lack of acceleration. In this case, the misfiring cylinders reduce the RPM, so the engine cannot generate enough power.
The driver can face a lack of acceleration even when pressing the acceleration. In rare cases, when multiple cylinders are misfiring, the car RPM would not go above 2000, and the speed would not exceed 30-40 miles (2). The drivers can also need more power when accelerating their cars after the initial startup.
Reduced Fuel Economy
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Another common sign of P0300 is reduced fuel economy. As discussed above, misfiring cylinders can both increase and reduce the RPM.
When RPM is increased, the cylinders fire the sparkplug more often, so the injectors need more fuel than normal. So, the drivers can suffer reduced fuel economy (2). Combined with reduced fuel economy, the drivers will face loss of power, hard startup, and odd sounds from their engine indicating that either one or more cylinder is misfiring.
Causes of P0300 DTC
Following are a few common causes of P0300 DTC:
Damaged Sparkplugs or Damaged Sparkplug Circuitry
Engine cylinders must fire the sparkplug continuously for seamless driving. However, if the sparkplugs malfunction, the cylinders cannot spark them, resulting in a slow combustion process and DTC P0300.
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Different factors can cause a sparkplug to fail, ranging from incorrect heat ranges to chemical contamination. In addition, 90% of the sparkplug fails due to improper torque, so proper installation torque is important to dissipate heat from the chamber and cylinder head. Finally, repeated overheating of the sparkplug head can also cause damage. So, a driver should avoid pre-ignition as it will result in heat in the combustion chamber leading to sparkplug failure (5).
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Another cause of P0300 is bad sparkplug circuitry. Although sparkplug circuitry is sturdy, repeated engine vibration can loosen electrical connections.
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In addition, the electric wires’ wear and tear can damage the circuitry, so a sparkplug does not operate. This causes misfiring in the engine’s cylinder.
The distributor Cap is Damaged or Misplaced
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Another common cause of P0300 is a damaged or misplaced distributor cap. A distributor cap is responsible for protecting the distributor’s internal parts.
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Further, it maintains the contact between sparkplug wires and the internal rotor, helping in effective combustion. So, a system malfunction leading to a bad distributor cap will result in bad ignition. The spark plug would not receive the spark from the distributor, so the air-fuel mixture would not ignite inside the chamber (4). Resultantly engine would not be able to produce energy efficiently, and the vehicle could face starting problems.
Damaged Gasket
A head gasket plays an essential role in terms of maintaining optimum engine temperature. When the gasket is damaged, the overall temperature of the engine increases, which can damage the sparkplugs and other components of the cylinder (3).
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Due to leaked head gasket, P0300 can occur as the engine temperature rises. A leaking gasket can also result in a decrease in the engine coolant level. So, the temperature would rise, affecting the overall engine performance.
Low-Quality Fuel
Sometimes drivers must consult the vehicle’s instruction manual while filling in the gas. They often fill the gas tank with low-quality fuel that contains lead particles resulting in engine knocking. The lead particles can be stuck between engine components such as sparkplugs, injectors, etc., impacting fuel flow and the entire combustion process.
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A lean condition in the cylinder can also cause P0300 DTC, mostly due to low-quality fuel and bad injectors.
Some vehicles might require high-octane, and filling those vehicles with low-quality fuel can result in high engine knocking. This will eventually cause misfiring in the cylinders.
Vacuum Leaks
Low fuel pressure in the engine can also cause P0300 DTC. In addition, the low fuel pressure results in engine misfires causing rough and idle engine conditions.
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Due to low engine pressure, the vehicle will not be able to travel long distances as the power generated by the engine is considerably low (1). A weak fuel pump can cause less fuel pressure in the engine. Furthermore, vacuum leakage can also reduce pressure within the engine, and the engine will generate less power. Vacuum leaks can occur due to faults in the housing, damaged exhaust pipes, etc. Vacuum leaks will also impact the air-fuel ratio inside the cylinders, which can cause P0300 and other DTCs.
Solution of P0300 DTC
Following are a few common solutions of P0300 DTC:
Change the Sparkplugs or their Circuitry
As discussed above, the sparkplug can cause this DTC due to improper combustion. However, you can replace the faulty sparkplugs at home. You can consult the instruction manual to determine the sparkplug specifications of your vehicles that can be ordered online. Usually, it is recommended that the drivers change their sparkplugs after 30,000 miles. Remove the sparkplug wires and COP (1) to change the sparkplug. You can unscrew the sparkplug using a keyset and replace them with new sparkplugs. Ensure that the new sparkplugs are tightened and the wires and COP are put back effectively. You are also recommended to test drive the vehicle to ensure the sparkplugs are working efficiently. Similarly, you can replace sparkplug circuitry if it is worn out to resolve P0300 DTC.
Replace the Distributor Cap
Another solution to this DTC is to replace the damaged distributor cap. A distributor cap is essential to protect sparkplugs and other components. Further, it also maintains contact between the sparkplug and internal rotors so the sparkplug sparks effectively. The distributor cap is usually located under the car’s hood near the engine’s center. Most manufacturers have painted it grey for easy access. It also has black cables connected to its spoke (4). So, you can replace the faulty distributor to ensure that the sparkplug is sparking effectively, resulting in a complete combustion process inside the cylinder.
Replace the Leakage Components
As discussed above, the leakage in different components can impact the air-fuel mixture. For example, the MAF sensor in this condition can send wrong information to the ECU resulting in a lean mixture inside the cylinder (3). So you can visually inspect the exhaust, muffler tip, and other hoses inside the hood. And you should immediately replace the leakage components to avoid the engine misfiring condition.
Reset the DTC and Test Drive
The last solution to this problem is to reset the DTC and test drive the vehicle. Sometimes, the ECU sends a wrong signal, and a wrong DTC occurs. For example, if the driver is not observing any lack of power or idle engine condition, reset the DTC and test drive the vehicle (3). The DTC can be easily reset by connecting hand-code reader with the OBDII module. The driver, in this case, should drive the vehicle for a few kilometers to check if the warning light does not appear again on the dashboard (4).
Common Cost to Resolve P0300 DTC
The following table illustrates the severity and the cost required to resolve the P0300 DTC:
Common Issues
Critical Level
Cost Required to Resolve the Issue
Sparkplug Issues
Intermediate: You can drive for medium distances with this problem. However, improper combustion will result in engine component damage.
$66-250 to replace the sparkplugs depending upon the number of sparkplugs to be replaced.
Vacuum Leak/Distributor Cap
Low: You can drive for even long distances with this issue
It costs $20-50 to replace the damaged intake pipes and hoses
Fuel Injectors
High: Driving along with faulty fuel injectors can damage the internal engine components
$1500-1900 to replace the faulty fuel injectors
Ignition Coils
High: Driving along with faulty ignition coils can result in the engine seizing
$230-640 to replace ignition coils.
Labor Cost
–
$20-200 to replace the faulty components.
Conclusion
To conclude, it can be said that P0300 is a severe-intensity DTC that indicates a misfiring condition in one or more engine cylinders. The common causes of this DTC include broken sparkplug, damaged crankshaft, damaged distributor cap, gasket issues, vacuum leaks, and low-quality fuel. So, if you are observing reduced fuel mileage and less engine power, it is a sign of misfiring cylinders. This issue should be resolved at the earliest to avoid internal engine damage.
There are many symptoms of a misfiring engine. The most common sign is an underperforming engine that needs to produce more power despite pressing the accelerator. Another sign is a rough engine start. In rare cases, the engine does not start, indicating that the cylinders are misfiring.
You can easily access sparkplugs under the distributor cap. First, you must remove the distributor cap around the engines. Then you have to unscrew the sparkplugs using the keys. Ensure that you order the new sparkplugs according to the manufacturer’s specifications. Otherwise, the sparkplugs may need to perform more efficiently.
Heating in the Gasket can be a cause of leakage. In addition, pre-ignition trouble could result in fuel combustion at the wrong time, which sends enormous pressure into the cylinder head, causing perforation and damage to the gasket. This will eventually result in misfiring cylinders.
