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????
I swapped the #3 cylinder spark plug with #2 cylinder and the #3 coil with #4 coil. I watched the live stream from the car computer and as the car was running, the #4 cylinder was active. I’m not sure what it means but there is a “value” that goes up and down. The #4 fluctuated while all of the other cylinders remained at 0. There is a total misfires number that continued to go up. I am going to move the coil over to the #2 cylinder and see if the problem follows. This suggests that the coil might be the problem and it would be worth replacing. Input regarding this information is appreciated. A couple of questions: What is the “value” that is going up and down represent? What coils do you recommend and should they be replaced as a set or would replacing only one be acceptable? I was asked earlier what brand of spark plugs I have. They are autolite. I have included a comparison between the #2 plug and the #3 plug. Thanks so much for the help…
as you stand at front of car, facing engine bay, yes: cylinder one is at your left (aka "front") end of the engine. Last link in my signature is the full engine section of the repair manual, should have that info. (On a phone turn it landscape to see signatures.) How long have you had the car? Addendum: just browsed the aforementioned "full engine section" myself, and could not find a diagram corroborating this cylinder ordering. But it's lore...
I bought the car new in 2012. I love the car and hope to keep it going for a long time to come. My son is going to a local college and uses it to get to school and other local activities.
EGR (Exhaust Gas Recirculation) system, including intake manifold, ever cleaned? If not, it'll likely be fully clogged, and has caused head gasket failure.
Sounds like you have a problem with the coil currently in #4 position. At close to 300K miles; IMHO - I'd go ahead and replace all 4 coils. Toss out the know bad one, keep the other 3 for future troubleshooting. Are those Autolite spark plugs iridium? Iridium plugs will go 100K+ miles w/o issues. re: spark plugs. The brown one is fine, the darker blacker one is burning some oil or running a little rich in that cylinder. Should probably run some injection cleaner with your next tank of gas; that might clean-out a slightly leaky injector issue. If the slightly blacker plug is from #3, that would explain the darker color - unburned, rich fuel mixture from intermittent misfires. Hope this helps....
A value of zero on a cylinder misfire counter means no misfires, while a higher number represents misfires per 200 revolutions.
