2013 Prius Misfire Codes

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the egr circuit should be cleaned no matter. see @NutzAboutBolts youtube video

 

If you have misfires, the first order of business is to find out why you have misfires. You've already worked on ruling out ignition as a cause, and to some extent fuel delivery (though dumping a cleaner in the tank is not really a thorough way of checking that). The main thing not covered yet is a compression or leakdown test, which will reveal whether you have some such issue as an early-stage head gasket failure.

There is some belief that proactively cleaning the EGR system might be a way to avoid head gasket failures. While that may be so, in the event that cold start misfiring has already begun, EGR cleaning isn't at the top of the to-do list now; finding the misfire cause is.

If a leakdown test implicates the head gasket, then the EGR should also be cleaned while doing the gasket job, so it's clean for starting up the engine with the new gasket.

If a test says the compression is fine, then you're back to looking for other misfire causes. You're right that EGR is designed to be closed at start and idle, so it is not normally a direct cause of misfires in those conditions, but now and then someone finds a valve that isn't fully closing.

 

Are you ever getting a severe engine rattling and shaking at cold startup? It can be occasional. I agree with Chapman, make the misfire go away before doing much else including any long distance driving. When you replaced the plugs did any of them look different, either cleaner or worse than the others?

Some unscrupulous sellers can use a head gasket/block sealer to minimize a leaking head gasket for a few weeks or months. A borescope can also be used to verify hg coolant leakage into the cylinder as well.

 

While it may be plausible as a cause if it happened, I don't really know that it happens very often. I guess I've seen a few reports where somebody said it did.

I don't think a sticking-open valve would lead to P0401. That code is really set for detecting insufficient flow, and even then, it can only be detected when the ECM's monitor routine runs (it gets snuck in during decelerations, above certain speeds, with the engine warm, etc.)

If you wanted to check that the valve moves smoothly in and out, the black plastic stator is held on just by two Phillips screws and there's not much in the way of taking it off. The screws are notoriously stubborn, but a hand impact driver or air-powered seized-fastener kit like Lisle's or Thexton's will knock them loose and then they come out nice as can be. (Note that those tools are not your familiar impact socket driver, which would probably break the screws right off; the right tool just bops straight down on the screw while you twist gently.) It's easy with the right tool; without, you're at risk of rounding the heads.

Then you could spin the rotor off counterclockwise and check that you can easily push the stem of the valve inward and it easily springs back out.

There was a whole thread where somebody had a P0401 because of a valve-not-opening-enough issue because the little ski jump molded into that rotor had gotten mangled. This is what it should look like:



But that involved pretty unusual circumstances (very hot climate, very hard driving, likely the EGR valve actually got hot enough the ski jump got soft). Easy to check, but also that one case is literally the only one I know of.

Overall, I would counsel most people to make a deliberate effort to remember other causes of misfires too and not overlook those, as a way to sort of balance the overweight attention to EGR on PriusChat.

 

With 290k I would get on leak down test. More info on Exhaust Gas Recirculation cleaning in my signature.