P0301 is a common OBDII trouble code that appears in the Toyota Mirai. It stands for:
P0301: Cylinder 1 → Misfire Detected
P0301 should be considered a cause for concern, and can be a threat to the drivability your Mirai. The one nice thing about P0301 is that it is a cylinder specific misfire code. This makes diagnosing the problems simpler than P0300, which means that the cylinders are randomly misfiring.
It will often be accompanied by codes P0302-P0308. These particular codes indicate that there is a misfire in one of the other respective cylinders.
Fixing P0301 should be a high priority. Driving with a misfire can damage that catalytic converter, and raw fuel will pass through the cylinder into the exhaust. Typically, fuel mileage will suffer as well.
Toyota Mirai P0301 Definition
P0301 is a cylinder specific misfire code, which means that cylinder 1 is misfiring and causing the code. An important thing to understand when finding the location of cylinder one is that it’s going to be the first cylinder in the firing order of the vehicle, and not the first cylinder that you might see when looking at the engine.
Mirai P0301 OBDII Code Symptoms
- The P0301 Toyota trouble code will trigger the Mirai’s service engine soon light.
- The vehicle itself may begin to run rough. It depends on how serious the misfire is.
- The vehicle may produce excess vibration, especially at lower RPM.
- Fuel mileage will suffer.
P0301 Trouble Code Diagnosis- Toyota Mirai
There are quite a few things that can cause the P0301 trouble code to trigger the Toyota Mirai . Here are the most common problems that will throw the code. They are presented somewhat in order from most to least likely to be causing the code:
- Bad Spark Plugs– Spark plugs are one of the most common causes of P0301. Take a look at the electrodes and see if they are in good shape. Most vehicles now come with iridium plugs that need changed very infrequently. That being said, the plugs are a great place to start. Here’s a great video on how to see if a spark plug is bad.
- Spark Plug Wires– On most modern engines, the plug wires are not nearly as long as they once were, but they can still go bad. Here’s how to tell if your plug wires are bad (video).
- Coil Packs– Coil packs rarely go bad, but when they do, they can certainly cause p0301 in your Toyota Mirai. Replacing a set can be very expensive. Here’s how to test them.
- Bad Fuel Injector– I you have a fuel injector that has gone bad, it won’t be able to properly atomize the fuel and you’ll get the P0301. Here’s a good video on how to diagnose an injector, but it can be a little tricky. This is definitely not the place to start.
- Vacuum leak– If your Mirai has a vacuum leak, it can be very difficult for it to get the right air/fuel mixture. This will cause the cylinders to misfire and it’ll throw the P0301 if the leak is around that specific cylinder on the intake manifold. It’s easy (and kind of fun) to chase one down. Popular Mechanics: How to find a vacuum leak.
- Cam or Crank Sensors– This one is very unlikely, but it does happen. If the ECU is not getting the right signal from these sensors, the vehicles timing is not going to sync up and it’ll misfire.
- Low Compression– If you have a leaking head gasket, bent valve, cracked head, etc.. that would cause compression to not be as high as it should, you’re going to get P0301. You should also feel the vehicle is down on power as well.
Most Common P0301 Fixes
If you follow the items listed above you should be able to fix the P0301. Here’s how to go about it:
Inspect and test the parts of the ignition system around cylinder 1 to determine whether or not you need to replace the coil packs, plugs, or wires. Most of the time that’ll be it. You can always reset the trouble codes and swap the coil pack, wire, and plug from cylinder 1 to another.
If you get a different P030X code, you’ll know that one of those three components is bad. Go ahead and replace them or have them tested. It’s an easy, and cheap method of determining if your ignition components have gone bad.
After that you would want to test the fuel injection system. There are links above that’ll show you how to do that. If that doesn’t work, it may be time to do a compression test and see if you have a leak in that cylinder.
Is P0301 a Serious Concern?
P0301 is cause for concern and left unfixed can get worse. Fixing the problem causing the code to fire can save you time and money and keep your Toyota from breaking down. Quick action may also save your catalytic converter from ruin.
Good luck diagnosing P0301 in your Toyota Mirai!