My 2012 Prius with 278,000 miles has a problem. The engine sounds awful and act like it is shaking off of its mounts. The check engine light is on. There is an unburnt fuel smell as the car runs. The engine oil dipstick seems free of coolant. The code from the computer is P0303. The scan tells me that the number 3 cylinder is misfiring. My reading of prior post suggests a possibility of a bad coil or a blown head gasket. Are coils something that should be replaced after a certain number of miles? I can replace them all for about 50 dollars. How do you tell if there is a blown head gasket? How do you suggest I proceed? Thanks so much for the help…
Swap the ignition coil from #3 and see if the problem moves. That would verify an ignition coil issue. ie. say you swap #1 & #3 coils and the code changes to P0301; that would tell you that coil is bad - since #3 cylinder is now firing. You can do the same with the injector and spark plugs; though that would be a lot more work. ONLY move ONE thing at a time while testing; so you don't have to guess which part actually failed.
Have you recently replaced the spark plugs? Did you get them off amazon or ebay??? If so, they are very likely cheap chinese copies. Coils last a long time. Mine have 382,000 + miles. Swoping the #3 and 4 coils is a good way to see if the coil is bad. If the miss fire stays at #3, it's the plug. Bosch plugs from Autozone have worked well for me. If the coil is bad, do not get cheap ones! Unless you like removing the windshield wiper assembly a lot. They likely but a few hundred miles. $12.50 for Prius coils, is extremely cheap! Check the coolant tank, is it at the full mark? If it is, the head gasket is likely okay, at least for now. Usually, the gasket fails between cylinders 1 and 2. But sometimes it's 3 and 4, but it's rare. You likely will never see water in the oil in a Gen 3 Prius. By the time that happens, you'll need a motor.
Thanks for the help… I changed the coil between one and three. Correct me if I’m wrong, I understand the cylinders are counted from left to right in order. I have some software on my computer to read the codes. Unfortunately, I can not tell if the information is new in that the number of misfires did not change from my earlier exam. Also the engine would only run for a couple of seconds before it would shut off. It did give me another code of P0302. It says that both codes are active. I have not swapped spark plugs or injectors yet. As to my coolant level it seems like it might be a little lower than the last time I checked it. I drove the car about 5 miles with the issue. It never ran great but at forty-five the engine vibration was greatly reduced. Would the coolant go down much with 5 miles of driving? Is changing the head gasket a difficult job? I am up for trying. I successfully disassembled my HV battery to get rid of the triangle of doom, changed brake rotors and pads and replaced the brake master cylinder along with general maintenance.
Did you clear the codes? I guess I had forgotten to tell you that. Why did you change 1 and 3? Why not 3 and 2 or 4? It's confusing.... Perhaps you should remove the spark plugs and look at them. And look down the spark plug holes and see if any of the pistons look cleaner than the others. And you can inspect the plugs as well. You can also use an inexpensive bore scope. And if you put pressure on the coolant system, you could see coolant leaking past the head gasket, if it has failed. Are you certain the engine is actually starting? The hybrid battery will turn the engine over for 15-20 seconds before disengaging. Do you have fuel in the tank? Perhaps check all the electrical connections, and check the fuel lines, you could have a leak. You did say you smells fuel. It does take some still to replace the head gasket. Have you ever changed a head gasket on any engine? It's the same.
ASRDogman…Thanks for the input. I watched a video on changing the head gasket and it is quite involved. At this moment the car is worth nothing so if I get another car I will keep this Prius and spend the time fixing it. Tomorrow I will go through all of your suggestions and report back. Thanks again.
Sounds like its not starting at all. A hybrid motor spins the engine so fast people often think the dngine is running. No
#1 is always the one closest to the harmonic balancer. Never use left or right references on the car, since most people don't know their left from their right. Depending on if they're sitting in the driver's seat or staring at the engine from the front of the car. Driver's side vs passenger side sometimes works too; unless your talking about a UK car vs US car. See what I mean????
