2009 Prius P0301 Code Diagnosed Gasket Replacement

Did they try shuffling spark plug and coil locations? Say swap cylinder one and four, then see if the misfire code changes to P0304.

 

This post is regarding my 2012 Gen 3 Prius with 182,000 miles with code P0301 and P0300, Misfire in Cylinder 1, poor fuel economy and power, and a smell of fuel inside the car which may or may not be perceived all of the time.

I had the same problem with my 2012 Prius Four. P0301. Misfire in Cylinder 1, which later became also P0300, Misfire in random cylinders. And a lack of power. And, terrible fuel economy; like around 35 mpg! I could also smell fuel at times. The car ran rough at startup. Coolant was not going down. Turns out that this problem mimics a blown head gasket. But if the coolant is not going down, that's not the problem. I thought it was the spark plug or the coil. Replaced all plugs and coils, but it ran worse after that. I would get the shaking engine when starting the engine, and now and then while driving, and I always felt the shuddering of the misfires which had spread to other cylinders, and especially when I tried to accelerate 'pedal to the metal' when max power was needed, and that made the check engine light (CEL) blink until I backed off. Interestingly, when the weather got really cold (air is denser), it seemed to run better. At first I thought it was perhaps EGR valve and PCV related. I cleaned the EGR, replaced the PCV valve, and cleaned the intake manifold. It ran better, but still had the error codes. I read more on here and thought that it must be an air/fuel ratio problem. Then I read that someone with the same symptoms replaced the MAP (Manifold Pressure Sensor) sensor connected to throttle body. This sensor is critical for the reason that it determines atmospheric pressure and reports to the ECU all kinds of information about the conditions within the atmosphere of the manifold, which it then reports to the ECU, and the ECU uses the information for controlling the air/fuel ratio AND the spark timing! I could have just cleaned the sensor, but decided I would buy a new one, which I installed. That was the problem! It was a bad MAP sensor that gave the ECU bad MAP data. I assumed that the bad data ran the engine too rich, which is why my fuel economy was so bad, and why I smelled fuel at times. My Prius ran perfectly after replacing the faulty MAP sensor, AND, my very first run after the fix got me 49.6 mpg fuel economy, and the power of the engine felt like it was a new Prius! This fix is easy. Lots of videos on YouTube show how to do this sensor replacement. Just remove the air intake and filter area to gain access to throttle body below. One screw holds in sensor. (The sensor has two holes, but only one screw is used, because the other hole is just a guide hole for a guide post.) You can literally be done with this fix in under 30 minutes. The sensor is about $200- online. You could always try to clean the sensor. I'm not sure what would be used or it is possible to clean it. So, make sure you know how to do this correctly before trying it, or you could destroy it. I hope this helps someone else. This problem persisted for months before I found the solution. Good luck everyone!

 

Do clean the EGR ASAP. First couple of links in my signature have info.

 

smart call not bringing in an older prius to the steelerships, IMO of course and as I read above maybe yours too.
Bein in Cali, if it were me, and I'd be looking to dig into the EGR passages first or second step as Mendel suggests above anyway.

I'll suggest beyond Mendel recommendation - that you take a look at and if it sounds like as good an idea to you as I think it might be, get your prius into gasket masters for a second opin.

The best in the business for what I've heard and the tubes I've watched and shared here.

Plus you'll learn way more about the entire process of how it happens and why it happens, which may also be beneficial to you as an owner of a gen 3.

I just picked this newest tube from their channel about a prius V ; take a look around to find one that is closer to what you are experiencing.

since you mentioned the engine swap above - just in case that becomes the reality, however unlikely and unwanted that news might be, gas mas is the place you might want to entertain that option as well.