Hello! I have a 2013 prius with around 150k miles. In the last week or so, it has had a very faint rattle intermittently at start up (sort of a flapping sound-- the first time it happened, I actually thought I had a flat tire). The check engine light came on and it is giving p0301 which I know can indicate head gasket failure. The coolant and oil are at normal levels and look normal. Just now I replaced the spark plugs and swapped the first and second ignition coil without replacing them. My understanding is that this way I can tell if it's just a bad coil (because the code would change positions). I tried to clear the p0301 code but can't clear it as it's permanent. Now here is where I'm confused-- does this mean that p0301 is definitively still an issue that the car is detecting? Or do I need to drive it around some and read the codes again to see? Any suggestions for next steps? I'm not particularly skilled at working on my car myself so I'll probably take it to a mechanic for anything more complex than spark plugs but helpful to know what this crew thinks!
it's probably the very beginning of a head gasket leak, but if you don't get the symptoms again, maybe it is the coils
Where did you swap the plugs? Since it's the #1 cylinder is where the code is, you could swap the #1 and #2 plugs. Then swap the #1 and #3 coils. Check the #1 plug and see if it's wet. An inexpensive bore scope that works with an iPad is good enough. If the cylinder is semi clean, you know the gasket is leaking. And with a pressure test, you likely will see the coolant leaking, if it's a head gasket failure. Seems like it might be just starting to fail, so you might not see a huge lose of coolant. Watch it EVERYTIME you drive the car. Check the levels everytime also.
Sorry, I meant to say I replaced the plugs! They needed replaced anyway. Then I swapped the #1 and #2 coils. I didn't notice any oil or moisture on the plugs but I can look into getting the scope. I don't drive all that much, probably have put under 15 miles on it since the first time I noticed the noise. Unless I'm likely to do damage, I'll probably drive it this week and confirm that the codes are still present and then take it to a mechanic for testing on the headgasket.
I meant to ask if you replaced them, but I got distracted while typing... Kinda surprised you can't clear that code. Perhaps you need to different reader? But if you get a misfire on #2, you know it's the coil pack. But that is not very likely. How many miles are on it?
