Check Engine Light On with rattling sound

It's likely your head gasket. Have you noticed your coolant level going down?
Don't waste your time with the spark plugs or coils.

 

I have to give Midas credit for understanding the egr problem, that’s more than most Toyota dealers do

 

It's easy to block off the EGR valve to check if it's sticking and causing the intermittent rough running condition reported. If you have a lead on a trusted mechanic ask him for check the trouble code(s) behind the check engine light and perform a compression leak down test to check integrity of the head gasket.

 

Don't do the EGR cleaning.

The codes were obviously cylinder 1 and 2 misfires, so they went with the simplest option of replacing the coils and plugs on those two cylinders, but the most likely issue is a blown head gasket which leaks coolant into those cylinders and causes the misfires.

At the very least ask the shop to focus on diagnosing a head gasket, but you should be figuring out the best option for getting the head gasket replaced, or moving on from the car. Dealers are definitely not it, I'd find either a trusted shop or look around for hybrid specialists and ask them specifically if they do 3rd gen prius head gaskets. If you get a head gasket done, ask specifically if EGR cleaning is part of the job, it should be.

 

EGR cleaning is its own service and never included with a HG repair.

 

It’s the head gasket.

 

EGR will be hopelessly carbon-clogged, is the likely cause of the head gasket failure, but where you’re at you need to deal with the head gasket first.

Reading between the lines, Midas mechanics likely saw the codes P0300, P0301 and P0302, which indicate general misfire, misfire in cylinder one and cylinder two respectively. And did pointle$$ coil replacement, missing the head gasket failure.

Advice? A 2011, it’ll have the low-tension, prone to oil-burn piston rings (how’s the oil consumption rate?). And it’s got a failed head gasket.

The EGR is about 200k overdue for carbon cleanout, thanks in large part to Toyota’s stonewalling. And that’s the likely cause of the HG failure.

If you’ve got to stay with it, what needs doing, with approximate costs, by qualified professional mechanics:

1. Replace head gasket ($3000 USD)
2. Replace short block ($3000 USD)
3. Clean EGR ($750 USD)

Keep in mind too: brake booster components are failure prone on Gen 3 ($3000 USD). Hybrid battery may be ok, but if it goes, another $3000 USD.

maybe just walk away?

 

I wonder somebody could come up with a metal screen/mesh filter mounted ahead of the EGR cooler that can trap carbon and keep the EGR system clean?

 

For 4th gen Toyota opted to connect the cooler downstream of the catalytic converter.

 

Admittedly I am new to the Prius community but not to wrenching including head gasket R & R on various engines over the years but I need a little help here. What I can't follow is the description of intermittent symptoms stemming from a failed head gasket. A compression check will reveal one or more of the cylinders with less psi than the others. Low compression could be rings, valves, or the head gasket so further troubleshooting should point to one or the other reason. If the combustion chamber(s) does not have integrity and cannot develop Toyota specified minimum psi per cylinder then that [those] low cylinder(s)s will never magically get minimum psi again and fire smoothly, only to rattle again the next cold start due to a bad head gasket. The engine will run rough all the time with a bad HG, will it not?

 

It depends on how bad the head gasket is. How long it sits, and how often.

If you catch it early enough, you can save the head from getting warped,
and/or throwing a rod through the block.

 

One of the early symptoms of a headgasket failure is misfire, but only on cold engine startup. The leak allows a very small amount of coolant into the cylinder, enough to "foul" the spark plug and cause the miss.

After some runtime, the plug is "blown" dry enough to work and the engine runs normally. Until the next cold start.

As the gasket gets worse, then you have problems with combustion gas getting into the cooling system (overheating, and low coolant), loss of compression, or hydro locking the cylinder (and bending the connecting rod).

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