Hi! I may be jumping the gun here but just wanted so expert opinions. I have a 2010 Gen 3 Prius. It had a blown head gasket 2 years ago, which was completely changed as a DIY (with supervision and help from a toyota mechanic, especially for the timing). The job was completed 2 years ago and I haven't had any trouble since with regards to engine issues and no longer had signs (car losing acceleration, kicking noises in engine etc). 2010 Prius with coolant and spark plug issue | PriusChat Yesterday, I got a P0300, P0301, and P0302 code. I have no signs of a cylinder misfire or worse (i.e signs I had at first cylinder misfire and eventual head gasket problem). It also says I have the P0300 code in permanence. Today, I'm gonna start looking at spark plugs, fuel injectors etc all the normal basic stuff potentially leading to a cylinder misfire. But I'm starting to get a tad paranoid and scared that it's going to be another HG replacement. So I wanted to know is it possible or common for a HG to fail twice? Are cylinder misfires commonly related to HG replacements 2 years after, or should I treat it as if it's just a cylinder misfire and not even think of the HG seeing as it was completely redone? When I changed the head gasket I also changed, amongst other things, : -all other gaskets in the felpro big HG kit -all spark plugs -1 fuel injector (because I lost the little black rubber piece)- I do not remember if it was a Denso or a fake -cleaned EGR -cleaned intake HG failure was at 133k KMs; I'm currently at 158k KMs. Oil from oil dipstick looks perfectly fine and antifreeze level is normal; no loss. Also want to add, a few months ago, I had an O2 sensor code that appeared on a really hot and humid day, and went away on it's own the next day and never came back. Was reading that a cylinder misfire can sometimes be related to O2 sensors so thought I'd mention. Thank you so much, I always appreciate the great help I receive here
I'd swap the coils/plugs around, see if the code follows. If not, borescope the combustion chambers, morning after a previous day driving. Preferably with cooling system pressurized. Make-shift coolant pressurizing gizmo: Also check condition of plugs.
"I do not remember if it was a Denso or a fake" You should find out. It could be the issue. You could always take the "O" rings and seals from the new one and put it on the original one. What about the spark plugs? Where did you get them? If they are the cheap chinese copies, they are likely bad. If you aren't loosing coolant, the head gasket is likely okay. Did you make sure the head was not warped?
Yes it can happen because in a simple gasket replacement not much has changed. With these engines a cylinder misfire is obvious at low or no speed Engine On but not as obvious at road speed Engine Ons. If it is a plug, coil or injector the scanner will show a rising number of misfires per cylinder as it drives. How many miles does it have and how many miles since the new head gasket? Oil burning rate in 5k miles (8k kms)? Was the head professionally rebuilt? Has it overheated ever and if so when? Has an egr flow blocking test been run to rule out a stuck open egr? The only good head gasket leak test is a quality borescope inspection when cold with coolant under pressure. However observation of a steam cleaned piston matching the misfire cylinder is not good anytime.
