P0300 - How To Repair: Meaning, Causes, Symptoms, Fixes

P0300 Code Definition

Random/Multiple Cylinder Misfire Detected

What Does the Engine Code P0300 Mean?

Character "P" in the first position of Diagnostic Trouble Code (DTC) represents the powertrain system (engine and transmission), "0" in the second position means that this is a generic OBD-II (OBD2) DTC. The "3" in the third character position in a DTC indicates that the ignition system is experiencing a malfunction or misfire has been detected. The last two characters "00" is the DTC number. OBD2 Diagnostic Trouble Code P0300 indicates that the random/multiple cylinder misfires have been detected. Misfires are detected whenever a cam sensor or crankshaft speed sensor measures and sends engine speed fluctuations to a Powertrain control module (PCM). This diagnostic trouble code (DTC) occurs in gasoline engines only. If you have a diesel engine, the section regarding the ignition coil/spark plug can be ignored, as your engine does not have these parts (compression ignition). In most cases, the error is related to the injection.

What Is the Cause of P0300?

While the most common causes of the P0300 code are worn spark plugs and faulty spark plug wires or coils, P0300 can also be caused by other issues:

Ignition coil defective

Incorrect ignition timing

Intake gasket leak

Incorrect fuel pressure and air/fuel ratio problems

Cable connection to ignition coil defective

Engine control unit defective

Internal engine failure

Injection nozzle/injector defective

Cable connection to injection nozzle/injector defective

Burned exhaust valve

Improper EGR valve operation

Insufficient cylinder compression

What Are the Symptoms of Code P0300?

Symptoms of a defect in the ignition coil/spark plug or injector:

The check engine light (CEL) comes on (also called a malfunction indicator lamp — MIL)

Very poor throttle response

The engine running poorly

The engine jerks when accelerating

A fuel smell from the exhaust

An increase in fuel consumption

Which Tools Are Needed To Diagnose P0300?

To find out more about the P0300 code that is generated and stored in the Powertrain Control Module (PCM) of your car, the only tool you need is the Carly Universal OBD2 Scanner, which works for all car brands in the world with an OBD2 port. Carly is a revolutionary solution that allows you to access your car’s data with your phone and translates this information into powerful insights, predictions, and possibilities. This saves you trouble, time, and money.

How To Diagnose and Clear the Code P0300?

Performing a diagnostics check with a diagnostic scanner helps you identify a particular problem area that is outside the normal range and shows where a fault might be occurring. This helps you to detect errors before they cause more damage to your vehicle. In comparison to generic OBD devices that only provide OBD-level engine-related data, Carly can run advanced manufacturer-level diagnostics, check all your ECUs in your car (like ABS, airbag, multimedia) and get deeper insights. You can find additional information about the trouble code and understand the severity of the problem. With the new Smart Mechanic feature, you get additional professional insights and tips from expert mechanics. You are able to check components and their mechanics, find detailed repair tips, and learn about potential future damage. After you have fixed the problem you can easily clear the fault codes with Carly, too. Also, the diagnostic results are safely stored inside the app or as convenient PDF reports you can share with your friends or a mechanic.

Common Mistakes When Diagnosing the P0300 Code

The most common mistake is to look and try to fix each individual OBD2 code without having a holistic approach. Understanding the interrelationship of OBD-II (OBD2) systems is crucial to determining the root cause of the problem and finding the right solution. For example, there are some seemingly unrelated causes that should be considered while diagnosing the P0300 code. For example, ignition misfires can be related to functional errors of the mass air flow sensor (MAF). As a result, either too much fuel (mixture too rich) or too little fuel (mixture too lean) may be injected. In rare cases, this can lead to combustion misfires, which is why the DTC P0300 is triggered. Additionally, keep in mind, that the OBD2 Trouble code P0300 indicates that random cylinder misfire is detected and it is very likely to appear together with other codes from P0301 to P0312, where the last 2 digits specify the number of the cylinder that is misfiring.

How Serious Is Code P0300?

OBD2 Diagnostic Trouble Code (DTC) P0300 is considered very serious. Besides unsafe driveability, ignoring this code can result in ignition failure, engine damage, an overheated exhaust, or the catalytic converter melting. P0300 fault code requires immediate attention and it is therefore recommended to have this code properly diagnosed and the problem solved as soon as possible.

How to Fix Code P0300?

The easiest test for this fault is to replace the ignition coil and the spark plug crosswise. This means that you take the faulty ignition coil from the presumably defective cylinder and install it on another cylinder. The ignition coil from the presumably intact cylinder is installed in the cylinder in which the defect was previously suspected. When this is done, the fault memory should be cleared and a test drive performed until the fault reappears again. Then read out the vehicle again. If the error is now stored on the other cylinder, the error has "migrated", which means that the ignition coil is actually defective. If the error has not migrated, the same must be tested with the spark plug. Here again, perform a test drive and re-evaluate the error.

If no fault is found during the "cross-exchange" test, it is recommended to check all cable connections to the ignition coil for defects.

Sometimes a power stage in the engine control unit that switches the current to the ignition coil can also be defective. However, this happens very rarely.

If all ignition system faults have been ruled out, the fuel system should be checked. If there are other faults in the fuel system, these should be repaired first so that a subsequent fault can be ruled out.

First of all, check the cylinder on which the error is located, whether the connector of the injector is properly seated, and check if it is damaged. If these are in order, the wiring harness at the injectors to the control unit should be checked. In addition, always make sure that the ground connection is also in good condition.

To check an injection valve for fault-free operation, it must be removed and tested on a test bench. It is recommended to have this test performed by a specialist. Normally, the test is offered by many Bosch service companies.

Learn More about the P0300 Code

Functionality ignition coil / spark plug:

The ignition coil has the task of transforming (converting) the vehicle's relatively low onboard voltage of 12 volts to the required high ignition voltage. The ignition coil then transfers the energy to the spark plug. The spark plugs ignite the mixture of gasoline and air prepared by the injection system in the cylinder. After ignition, the gasoline-air mixture generates a steady explosion pressure, which forms the basis for engine propulsion. Each cylinder has its own spark plug. Some vehicles even have two spark plugs per cylinder (e.g. Mercedes). To ignite the mixture, the spark plug produces a spark at one or more ground electrodes located on the thread of the spark plug. Inside is the required counterpart — the center electrode. Both are separated from each other by the white insulator made of ceramic so that the spark must jump from the ground to the center electrode. With this spark, there is enough heat to ignite the mixture.

How the Injection Works:

The injection is a valve that injects fuel into the intake tract/intake manifold or directly into the combustion chamber (direct injection) on an internal combustion engine. Nowadays, gasoline and diesel engines mainly use electrically actuated solenoid valves. With direct injection, the fuel is sometimes distributed over more than ten injections.

*Every car is unique. The Carly Features that your car supports depend on the model, build year, hardware, and software in the car. Plug the scanner in the OBD2 port, connect to the app, run your first diagnostics, and check which features are available for your car. Also, keep in mind that any information provided on this website is for informational purposes only and should be used at your own risk. Mycarly.com is not responsible for any errors or omissions, or for the results stemming from the use of this information.