Prius Shake when coming off idle, and/or at low RPM

P0301
Misfiring in a cylinder can be due to a number of reasons.
Coolant entering the cylinder through a ruptured head gasket.
Malfunction of spark plugs and ignition coil, incorrectly adjusted fuel and air supply system.

Have you ever cleaned the EGR system?
How often do you check the coolant level in the engine?

C1464
C1465

These errors may have subcodes that will indicate problem areas.
Specify whether the codes are frozen or current?
Do these error codes appear again when the DTC is reset?

Are there any signs of rodents under the hood of the engine compartment?
C1464/C1465 ABS code, ABS, Brake lights on and no speed | PriusChat

 

Head gasket failed, last year. Because you put in the clogger stuff,
you'll need a new radiator, heater core, water pump and thermostat and will
still need to flush out the coolant system, including the head, and pre heater
under the car through the exhaust....

The "C1464 and 5" codes are for the ABS system I believe.

 

Look here. Well explained in the post. Mendel Leisk
Bad Flywheel | PriusChat

 

Are you having overheating issues?
Some use white vinegar to try to clean the clogging crap out.
And yes they are expensive, but the labor to do it is more expensive.
Which will make your "mechanic" happy.....that's probably why he said
to use it. I take it you have a head gasket failure?
Replacing it is the ONLY way to fix it.

You have to weigh all your option about keeping or selling the car.

 

Cleaning the EGR now, is akin to rearranging deck chairs on the Titanic. Deal with the head gasket first.

if you follow through with that, do clean the EGR. There’s links in my signature regarding head head gasket replacement and EGR cleaning. Bottom link is full engine section. (On a phone turn it landscape to see signatures.)

FWIW, “some” sealer products can supposedly be dissolved and flushed with a 50/50 water/vinegar mix.

Could be. 260k miles, head gasket long blown, held together with sealant. Sell with full disclosure.