Scanned the check engine light trouble code with an OBD-II scanner and found misfire code p0300: Random/multiple cylinder misfire detected?
Want to know about engine code p0300 means, causes, fixes, and more?
We show you:
- What is the cause of the p0300 code?
- How to fix the problem and get the check engine light to turn off?
Then stick with us here at Proper Mechanic because we are on a mission to solve all of your vehicle's problems in record time.
What Does The p0300 Code Mean?
This means that two or more misfires are happening in your engine.
A misfire happens when the fuel/air ratio is off.
Many things can throw combustion out of normal operation.
What Caused The p0300 code (Possible Symptoms)?
Here are some common causes of the p0300 code that you are now searching for:
- faulty spark plugs
- vacuum leak/broken or disconnected vacuum hose
- bad/dirty mass airflow sensor
- faulty fuel injector
- bad battery
- clogged fuel injectors
- clogged catalytic converter
- a bad crankshaft position sensor
- EGR valve stuck open/EGR system problem
- a faulty camshaft position sensor
- bad coil packs
- low compression
- bad exhaust valve/intake valve
As you can see, there are a lot of possible causes for this p0300 diagnostic trouble code, and finding the problem is a process.
Here are some of the symptoms you will notice :
- rough idle
- loss of power under load
- check engine light blinking
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How To Diagnose A p0300 Code?
Diagnosis of this specific engine code requires more or less checking over the whole engine to see what's going on.
The best automotive technicians are like doctors, and their cars are like their patients. They give each car the love and care it deserves by paying attention to all of its little functions. Finding a misfire can be tricky.
But we know you'll be able to pin it down.
Shown above is Scotty Kilmer giving you the lowdown in this ridiculously simple guide on how to fix this code, and he nails down the basics of this repair in this video.
Step 1: Ignition System Check
When your engine misfires, the ignition system is the first system to inspect.
Remove the ignition coils and inspect the spark plugs for fouling. Check the gap of the spark plugs.
Turn the ignition on and test the electrical connectors that go to them to make sure they are getting 12V power.
Vehicles with an older ignition system rely on a distributor cap and distributor rotor for delivering electricity to each spark plug at the right time.
Step 2: Check For Vacuum Leaks
Check the intake manifold and all hoses around it. In newer vehicles, we are starting to see more and more plastic intake manifolds, and it is not uncommon at all for them to crack or for its gasket to fail.
Spray soapy water around the intake manifold gasket while the engine is running and looks for bubbles. A leaky intake manifold causes all kinds of misfires.
Each vehicle has a different system of air passages that have to run healthy. Check parts like the PCV valve, EGR valve, mass airflow sensor,
It's also possible to check for vacuum leaks by
Some of the air hoses are made of plastic and easily break after they are heated up for extended periods.
Step 3: Check For Fuel Pressure
- Test Fuel Pressure
Lack of fuel pressure causes a lean condition and the engine misfires when this happens.
- Fuel filter
Changing the fuel filter out first is the least expensive move. But don't worry, even if you do buy an expensive part that didn't need to be replaced you can still get your money back in a lot of cases.
- Fuel injectors
Water vapor can get inside of your fuel injectors and inhibit their function over time.
This can cause misfiring. Servicing the fuel injectors every 60-100 thousand miles is something that all experience automotive technicians do.
- Fuel pump
If the fuel pump is weak and failing then your vehicle will randomly misfire because of its lean running condition.
- Fuel pressure regulator
Inspect fuel pressure regulator and seals.
Step 4: Check Sensors/Battery
The whole OBD2 diagnostic and performance system relies on the battery, and the engine relies on various sensors that tell its computer
- crankshaft position sensor
The crankshaft sensor is located somewhere on the bottom side of the modern engine, and it monitors the position of the crankshaft.
- camshaft position sensor
Locate and inspect all camshaft position sensors and wiring.
Step 5: Check Engine Timing And Compression
Some engines have a timing belt instead of a more sturdy timing chain that connects the crankshaft with the valves.
This belt needs to be serviced every 60-100 thousand miles, and if it slips out of place your engine timing will be off, and misfiring can and probably will occur.
Testing the compression on each cylinder verifies that the engine's piston rings and valve seals are functioning properly.
If there is a bad valve seal, blown valve, air leaking from the engine head, the pistons rings have worn out you will know it because it will fail the compression test.
Read More >> How Often Should You Change Spark Plugs?
How Do I Fix An p0300 Code?
For all of these repairs, it is ideal if you have the specific vehicle's service manual, but there are also systems like ALLDATA that have almost any vehicle's specs and guidelines.
What you should also take in
Potential Fix 1: Replacing The Spark Plugs
Spark plugs need to be serviced every 20-100 thousand miles depending on their quality and correct installation.
They are also one of the main causes of this engine code.
You can replace the spark plugs in your vehicle by removing the engine cover(if there is one), removing the ignition coils, and using a spark plug socket to carefully remove each spark plug.
Remember to always double-check the spark plug gap before reinstalling, and always use a torque wrench to torque the spark plugs to spec.
Potential Fix 2: Repair Vacuum Leaks
The procedure for fixing a vacuum leak varies depending on where the problem is;
For example, if you have found that the air intake or its gasket needs to be replaced, you'll have to unbolt the fuel rail, unmount/unclip and remove the fuel injectors and replace the intake or the intake gasket.
Always torque down the air intake in the right order upon reinstallation.
The vehicle-specific service manual will help aid in a successful repair of this p0300 code.
Other vacuum hoses and other air-related valves may simply be broken, unplugged or improperly routed. Follow the vacuum system like a map, and trace everything to the correct spot.
Potential Fix 3: Fixing A Fuel System Problem
Get your hands on a fuel pressure tester and test the pressure of the fuel in the fuel rail.
- Fuel filter
Replacing fuel filters is a pretty simple task in most vehicles, but accessing them is another story because sometimes they are in hard to reach locations.
Nonetheless, the fuel filter is simply a filter between two fuel hoses.
- Fuel pump
Fuel pump making strange whining noises? Use the vehicle's service manual to remove and replace the fuel pump.
- Fuel pressure regulator
The fuel pressure regulator is easy to find on the fuel rail of most engines, and it's typically clipped in with a metal clip that you have to pull out.
Potential Fix 4: Battery Check
It never hurts to check the battery.
Visit your local auto parts store and have the attendant run a quick check with a battery tester to ensure that the engine is running with full power.
Replacing the battery is simple, and it is typically mounted into where it sits with a bolt or two; disconnect the negative terminal first to avoid a short circuit and then the positive.
Potential Fix 5: Timing Belt Replacement/Engine Rebuild
Servicing the timing belt is a more intermediate task because it requires removing some panels, timing belt tensioner, etc.
Reference the service manual specific to the vehicle on how to service the timing belt on each specific vehicle.
Removing/installing parts in the right order is crucial when repairing the timing belt!
And let's face it, sometimes there is no easy or simple solution to the problem. Like if a cylinder fails a compression test; more wrenches come out of the bag.
We encourage you to have the confidence to fix this p0300 code yourself!
Ask us any questions and you'll quickly be answered with quality advice about your auto repair.
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How Do I Fix A p303 Code?
When problems like a misfire happen in your vehicle it requires you to search for the problem to find a proper solution. Here are the reasons why your vehicle could be misfiring on its third cylinder:
Potential Fix 1 - Replacing the Third Cylinder Ignition Coil/Distributor cap
Replacing the ignition coil is about the easiest way out of this check engine light pickle.
Don't want to pay a lot of money? Buy one on Amazon or even pull one from a salvage yard.
Potential Fix 2 - Replace Spark Plugs
Replacing the spark plugs is a must-do when maintenance, and even if the misfire problem isn't the spark plugs, after all, your vehicle could be due for replacement anyway.
Treat your car like it's yourself; because it is, it's an extension of you.
Potential Fix 3 - Perform A Vacuum Test
Replace the intake manifold/gasket according to the vehicle's service manual. Torque the bolts down in the correct order.
Use your vehicle's service manual to check all vacuum line connections. Fix any broken vacuum lines and reassure that everything is connected correctly.
Potential Fix 4 - Electrical Repair
Replace fuses/battery if necessary.
Repair any electrical wires.
Check your vehicle manufacturer for recall campaigns calling for the replacement of the PCM due to this code.
Potential Fix 4 - Compression test
The next step for diagnosing an engine misfire would be measuring the PSI of the cylinder with compression tester or leak down tester.
You can find a compression tester at your local auto parts store or on Amazon for relatively cheap.
Simply install the tester into the third cylinder like you would the spark plug, unplug the fuse to the fuel pump so the engine doesn't start up, and crank the engine over as if you were going to start it.
If the cylinder tests for low compression (anywhere below 100 PSI), you can then conclude that the engine has either a leaky valve or a bad piston ring, and needs rebuilding. There is no easy fix to this problem.
Reset the check engine light with a scan tool or by simply unplugging the negative battery terminal for a few minutes.