How to eliminate P0401 after Gen4 engine into Gen3 ?

from what i've read, that's the one problem no one has been able to overcome.

all the best!

 

A few things here. P0401 is a code for insufficient flow, which is the opposite of what you normally get when you put Gen 4 valve and cooler on Gen 3 exhaust. The Gen 3 exhaust supplies a higher pressure, and the Gen 4 cooler/valve are oversized for that, so the normal result in that configuration is excessive EGR flow.

So your situation necessarily has more than one thing going on.

Make sure you undo that, if you haven't already. The effect of the wire swap is only to disable the EGR valve completely (but in a way that avoids triggering P0403). It will, of course, trigger P0401, not immediately, but as soon as the ECM runs its monitor and detects there's not any flow.

The wire-swap was apparently devised by somebody looking for a way around the excessive-flow problems inherent in using the Gen 4 valve/cooler with Gen 3 exhaust. Disabling EGR with the wire swap definitely eliminates the excessive-flow problem. Of course it creates an insufficient-flow problem instead, and by suppressing the P0403, it also suppresses the fail-safe timing adjustments that the ECM would otherwise make to protect the engine when it knows EGR isn't working.

More on the pin-swapping business in this post and those preceding and following.

For whatever reason, after somebody came up with that wire swap as a covert way of disabling EGR to avoid an excess-flow problem, it started getting "explained" on PriusChat as Gen 4 having somehow changed the pinout of the valve, which is baloney.

So, after first making sure any pin swapping is put back right again, are you able to confirm the valve's operation using the active test in Techstream?

As soon as that is working, you ought to find yourself with excess-flow symptoms (idle ok and full-throttle ok because valve closed then, mid-loads lousy because too much EGR).

From that point, you can start working on solving that problem. The most promising thread I've seen on that so far involved making a thin sheet-metal plate for between the valve and elbow, and trial-and-erroring the size of holes in the plate to try to reduce the excess flow by the right amount.

That was a recent thread (in the last half-year or so, if I remember right) but I'm having no luck searching it back up at the moment.

 

@ChapmanF I believe you are referring to Page 3 in this thread, correct?

Advice on gen 4 engine into gen 3 | Page 3 | PriusChat

 

Yes, that's the one! Thanks for finding it.

The money shots are in this post.

What I'd like to see is somebody who does that, with a few different hole sizes, and posts the resulting EGR flow test numbers to see how close they get to unmodified Gen 3s.

Hardware stores often sell small sheets of thin stainless in a "hobby metals" section. I would probably be looking at that, rather than aluminum, for the material.