EGR code: can I cap the EGR port temporarily?

Where exactly did you get that "understanding" ?
I don't believe that is true at all.

I suggest that just letting it GO until you can get it serviced would be much preferable to screwing with it.

 

There is a prevailing theory on PriusChat*, which is that, over time, (1) the EGR passages become more and more clogged, and pass less and less EGR, and that (2) an effect of EGR is to lower combustion chamber temperatures, and therefore (3) the reduced EGR from clogging leads to higher temperatures there, leading to (4) damage to the head gasket.

If that theory is right, then by capping off your EGR entirely, you would effectively be going 100% clogged, and saying "yes, world, hit me with the head gasket NOW!".

Maybe that's worth a second thought.




* about the prevailing PriusChat theory, I can't say I'm entirely convinced yet; there are some bits that I'm not sure add up, and I've posted once or twice on threads about it asking for pointers to any genuine hypothesis testing that's been done about it, and drawn only tangential responses so far. But that doesn't get in the way of being able to say what the prevailing theory is.

My questions about the theory come mostly toward the tail end; I'm like "(1) of course, (2) uh huh, (3) ok ..., (4) um, numbers?"

 

How many miles on it?

Engine coolant level in the reservoir stable so far?

As @ChapmanF said, fur crisakes don't cap it off. Get on it as soon as practical. Or don't...

 

@ChapmanF is correct. Just to make things more clear: #1-3 is proven and #4 is an outcome not proven yet. But, I'd add a couple more hypotheses:

5. The EGR pipe inside the intake manifold plugs up and doesn't distribute the EGR gas to the #1 cylinder. The #1 cylinder is furthest away from the EGR inlet pipe. Cylinders closest to #1 develop a lean condition which ruins the head/head gasket. This theory is supported by both anecdotal head gasket failure and intake manifold cleaning stories on PC.

6. The engine overheats and warps/expands the plastic rotor in the engine coolant pump causing a pump failure. The engine coolant pump failure overheats the engine further and damages the head/head gasket.

Pixel XL ?

 

That's a lot, maybe a record.

Take an hour at least, do this:

This will give some idea what you're dealing with. Post some pics of how it looks, if you can.

 

To your knowledge, has the EGR been cleaned/replace previously or no?

That is an incredible amount of miles if it has never been touched....for a 2010

 

I too am interested in understanding the apparent connection between EGR and HG failures on these cars. BTW, not that it's going to stop me from doing a thorough EGR cleaning pretty soon (at about 60k miles on my 2012 now).

Wondering if it could be related to mjoo's item #5 - that the problem is not so much that EGR would be removed completely, but that if it somehow were affecting different cylinders differently.

 

Meed More comparison of non-eco cars vs eco car please, not enough evidence.

 

1) The 1.8 L engine on a Prius is really a bored out 1.5 L leaving less room for the head gasket.

2) The EGR on a Prius is cooled. The cooler is the part most likely to plug up. Not only does the EGR reduce the combustion temperature, but it is cooled to improve the thermodynamic efficiency of the engine. When the EGR plugs up not only do you lose the reduction in combustion temperature from the recycled exhaust gas, but also the reduction in temperature from the cooler.

That combination is murder on the head gasket. I have yet to see a post from someone who has a failed head gasket, but didn't have a plugged up EGR. And, there have been a large number of posts along the line of "Help my head gasket failed." or they have the symptoms of it.

I also do not know why the emissions control people are not on this. A plugged EGR should cause an increase in NOx emissions. But, most car smog checks only verify that the computer is working and not throwing codes. And of course a Prius with these symptoms does not throw a code until you get to the cylinder misfire. At that point it is too late. The head gasket is gone.

Many people then buy a new car. Maybe that is Toyota's plan.

 

That's all been posted many times before and I'm familiar with it, but it's still unresponsive to the "um, numbers?" question.

Suppose the working cooled EGR drops combustion chamber temperatures from 900 to 825. If the gasket data sheet says "don't run this gasket above 850" that would suggest one interpretation, and if it says "don't run this gasket above 1050" that would suggest another.

I just shamelessly made all four of those numbers up, because I don't know even in the ballpark what they really are. I am sure there are people who do and can cite sources. It's just that, wherever those people are, none of them have ever posted on PriusChat yet.

The car also does an active test for EGR flow.

 

ne idea how often?
after every cold start?

 

Happens during coasting/deceleration while driving. Those are conditions where the fuel is cut to the engine, and it is sucking against a closed throttle, creating a deep manifold vacuum, which the manifold-absolute-pressure sensor detects. The engine has to be at operating temperature, doing 950 to 1600 rpm, and have been in fuel cut/deceleration for two seconds or more. The car then opens the EGR valve some and watches for the MAP sensor to show the manifold pressure increasing, which seems like a pretty positive confirmation of flow. If the pressure doesn't change by at least 1 kPa and that's detected on two consecutive trips, P0401 is logged.

I do not know how often the ECM performs the test. For the 2-trip detection logic to make sense, "at least once a trip" would seem plausible.

I wonder if maybe they copy-pasted the test logic from a non-hybrid model? Maybe sometimes in a Prius you make a trip where you don't ever have the engine doing 950 to 1600 rpm in fuel cut for two seconds or more after warming up, because it just stops instead. Then maybe even if the previous trip made the first detection of a problem, this trip doesn't, so the 2-trip logic prevents the code being logged.

Maybe it's not a bad thing to coast in B for several seconds every now and again, and do it two trips in a row.