2010 Prius makes loud noise and now will not crank

Does it go to Ready? What is the voltage on the 12v battery? Do you have Check Engine or other warning lights? Do you have an OBD2 code reader?

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Did it sound like this?

 

How many miles?

 

How did you determine that 12v battery is good?

 

The typical severe knocking and rattling on a 2010-14 is usually a head gasket failure. Especially if it happens on a coldstart and clears after a few seconds or a minute. Liquid gets into the cylinder and fouls the plugs. A lot depends on how long this has happened. When its bad the passenger side coolant reservoir will start going low. Usually no coolant in the oil or white smoke. White smoke means it is extremely bad.

Most likely disconnecting the 12v battery for a minute will reset errors. It needs repair now. If the engine was burning a lot of oil, also common, it needs another engine, ideally a lower mile rebuilt.

Don't spend a lot of time changing parts without first determining if its a headgasket with a borescope. Here is what can happen if you decide to wait and see.

 

are you shutting the car off, before it has finished it's first warm up cycle ?

you can have weird knocking if the engine hasn't finished it's first warm up, and is shut down while it's running.

otherwise, I would expect a head gasket in it's future. don't continue to use the car if the head gasket is failing, it will fail catastrophicly , and cost more to replace the entire engine, instead of just the head gasket repair

 

That's the Prius "Death Rattle."

It's just possible that you can fix this before the gasket lets go.
I'd check the oil for signs of coolant contamination, if it's clear I'd consider looking at the EGR circuit.
If you do not know what this is, do some reading.
You may be experiancing the first twinges of an event caused by the automotive equivalent of a clogged left anterior descending artery (LAD).
It sometimes goes by a less geeky nickname:
The Widowmaker.

The pattern usually goes something like rattle...cylinder misfire code...change plugs, change coil packs, change owner (or...engine)

If you decide to get the plugs anyway, get them from dealer stock or a large parts house.
There are a lot of fake Densos out there....especially from the Amazon.

Of course....if I'm right, then the knock-off plugs will be good enough for your purposes.....

Good Luck!

 

Likely head gasket failure in progress, aided and abetted by clogged EGR, with assistance from PCV effluent. See my signature for more info on dealing with that.

I'd get a leak-down test done, as soon as practical, hopefully before a piston arm gets bent, or the damper between engine and transaxle breaks. Plus the previously mentioned boroscope inspection is good,. Cylinder one or cylinder two are the usual culprits (cylinder count starts from "front" of engine, end opposite the transaxle and inverter).

 

bummer

 

The often-overlooked AECS story strikes again!



The best thing about that video Krall posted is that it identifies most of the usual causes of misfiring. Not everybody will find that the spark plugs are the cause, in their own car. Some will have to work through more of the usual suspects. But it is always good to remember that (1) misfiring in a Prius sounds horrible, whatever is causing it, but (2) some of the things that cause it aren't horrible to fix.