Check Engine Code P0301

Are you struggling with check engine light code P0301? Learn what causes this fault code and how to fix it with advice from an experienced mechanic.

Troubleshooting code P0301 (and other P030X codes such as P0302, P0303 etc.) is easier than most would expect because your vehicle's computer has already figured out which cylinder that is having problem... saving you a lot of diagnostic headache.

Misfire codes (P0302, P0303, etc.) are some of the most common OBD codes. They basically mean that there is a misfire on that respective cylinder in the firing order. For example, P0306 means "misfire cylinder 6", P0302 means "misfire cylinder 2" and so on.

If your car has one of these codes you need to get it fixed asap. If you choose to drive your car in this condition you will do damage to the catalytic converter.

Driving with a misfire causes unburned fuel to be put into the exhaust (because there is one or more cylinders that are not burning it like they should) which then is sent to the catalytic converter. It is not made to clean up exhaust with unburned fuel in it and will soon become faulty. This is an expensive repair so the best thing is just to get your car repaired! Let's see what are common causes and fixes for this trouble code:

Spark Plug Close Up

What Causes a P0301 Code?

  • Spark Plugs and Wires
  • Fuel Injectors
  • Internal Engine Problems such as Low Compression, etc.

Less Common Causes

  • Faulty Computer
  • Coil or Coil Packs
  • Crank or Cam sensors or reluctor wheels
  • Faulty O2 (Oxygen) Sensors

To troubleshoot, repair and maintain your vehicle, you'll need diagnostic and repair information that is specific to your car or truck. For this I personally use and recommend ALLDATAdiy. With full manuals for over 30,000 vehicles online, you will find an exact match for your vehicle's year, make and model.

Besides being cheaper than a factory manual, they also offer step by step repair instructions and detailed diagrams beyond what is found in most printed manuals. Click here for a sample of their diagnostic and repair information.

How to Fix Engine Code P0301

1. Inspect the Problematic Cylinder

The first thing to do if you have this code is to inspect EVERYTHING that has to do with that specific cylinder. Since the misfire code is for that cylinder only it has to be only something that would affect that cylinder and not the others. This is the key to diagnosing this problem.

You want to be looking at the spark plug, wire, coil and injector of that cylinder. You also perform a compression test with a compression tester kit... followed by a leak down test using a leak down tester to see if your piston rings or cylinder head valves are getting worn and causing low compression.

A good way to check the plugs, wires and fuel injectors is to switch them with different cylinders to see if the misfire moves with them.

2. Swap Parts with Other Cylinders

Some of the easiest ways to diagnose this OBD code are to change parts. In order to figure out if the check engine light code P0301 (misfire on cylinder 1) is being caused by a fuel injector, you can (in most cases) just switch it with a different cylinder.

So if you switch the fuel injector from cylinder #1 (because of code 0301) with cylinder #3 you can then start the vehicle and let it run. When the check engine light comes back on you just read the codes again. If the code that comes back is p0303 then you know that the problem is the injector and you need a new one.

This method works for lots of things. You can use it with spark plug wires, ignition coils (assuming you have a coil for each cylinder), spark plugs, etc. If you have a coil on plug system (COP) then you can just switch the whole assembly with another one. This diagnosis method works for any P0xxx code.

Remember this type of code is one that cannot wait long for you to attend to. You will likely notice lower fuel mileage, loss of engine power, blinking check engine light and probably others too. Since there is a misfire, that means that raw fuel is going into your catalytic converter. The CAT is not made to process raw fuel. It will not take long for the CAT to go bad and if it does you are looking at a min. $500 repair bill.

If you still have any unresolved vehicle problems or questions, you can ask an auto mechanic online. For expert answers specific to your vehicle's make and model, I recommend JustAnswer Car. They have a large pool of certified mechanics to answer your questions for a small fee and you can also browse their answers to other users for free.

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