P0401 - Check Engine Light (entire system cleaned and new EGR Valve)

"What does the P0401 OBD-II diagnostic code mean? Also known as insufficient EGR flow, this particular OBD-II trouble code indicates the engine control module (ECM) has detected the exhaust gas recirculation (EGR) valve is not allowing sufficient flow of recirculated exhaust gases into the engine."

 

What any Toyota trouble code means is what is written in the DTC Detection Condition box in the section for that code in the repair manual. So for this one, it's:



In other words, there is a self-test the ECM runs sometimes, by sneaking it in when the engine is turning with the fuel cut off (as when going down a hill). Under those conditions, the ECM can open the EGR valve a little, which should make the Manifold Absolute Pressure reading go up, and then close the valve, and the MAP reading should go down again.

The difference (MAP reading with opened valve − MAP reading with closed valve) is saved as the result of the test. The most recent saved result can be checked, as seen in this thread.

If that test result gets too small (opening the valve doesn't make enough difference), the P0401 code is set. So it might mean the valve isn't opening enough, or it might mean there's clogging somewhere, or it might mean the MAP sensor is wonky. Knowing how the test is done often helps in troubleshooting what might have caused the failing result.

Other sources on the internet that offer to say what a trouble code 'means' are often not as helpful as looking up the code's actual detection condition.

 

You got the small (~1/4” ID) EGR passages, one per port?

What’s the miles?

 

Hello @Rob Cameron, were you able to resolve the issue? My car is showing the P0401 CEL code a few weeks AFTER I did a (preventive, no issues, no CEL lights whatsoever) complete EGR system clean up.

 

What was the miles, and was it the first cleaning? You got the intake manifold EGR passages too?

Did you manage to get the cap off the EGR valve? If it's relatively long in the tooth, there's a "ramp" portion at the bottom of a cylindrical black plastic cup inside the cap of the valve, that can get worn, messes up the action of the valve. Just speculating, an EGR system with long-neglected cleaning may wear out that ramp sooner?

 

The ski-jump circled in Mendel's photo above is still good. When it gets a rut through it, it's kaput.

 

@ChapmanF Thank you for the help, do you mind explaining (or pointing me to the post that does explain if it has already been done) how the ramp works? Somehow it seems to me that just a solid bump to mark the stop of the magnet should work but I guess I'm not understanding how it works, thanks again!
EDIT: Here is @ChapmanF gracious response and explanation from my thread in case that someone is wondering the same thing I was:

 

Did you ever get the EGR update package and PCM update per TSB 0027-16?

 

I don't know, how do I get it? How can I check.

I think I found that my issue was actually the ramp looking plastic inside the EGR Valve magnet being worn out. I replaced the magnet with another one and the code has gone away for 3 days now. I still think I should get the update, please let me know. Thank you!

 

So is the part with the “ramp” magnetic? I’ve had it in my hands, just never occurred to me. Just yesterday I was looking at the pics (I posted), trying to understand how it all works. Ultimately the object is to reliably open and close the valve.

 

Yes, it's the rotor part of a stepper motor. The black cover you took off to get to it is the stator.

 

@Mendel Leisk I'm glad I wasn't the only one!
I'm still not sure what is the purpose of the "ramp", I think it just might be stronger/easier to manufacture that way?

When the stator gets charged, it moves the electromagnet. It will try to keep moving/closing (if commanded to do 111[?] steps when is not fully open) so the taller end of the ramp catches with the stop on the bottom round part of the threaded rod and makes it stop.
When I "play" with the bad magnet, I can feel how if I thread it very lightly it will stop and unthread by itself when let go as it should. However, if I thread it a little harder, it will get stuck on the worn plastic stop (ramp) and when I let go it will fail to unthread by itself.
If I take the magnet spring out, the magnet goes low enough to let the damaged ramp make full contact with the metal stop of the threaded rod so I can not feel it getting stuck unless I lightly lift the magnet (simulating the spring force upwards) then I can feel how it catches and gets stuck.
I believe that could be why I didn't get an error until a few weeks later instead of right away, the magnet could have been function correctly intermittently and only when it got really stuck the computer threw the error. I'm still going to try to repair the ramp on the spare EGR valve that I have, I think "welding" the same plastic back would be ideal but I'm not sure I have enough to do so. I might have to reluctantly introduce a foreign plastic to rebuild the ramp, not sure epoxy would work.

 

Right, while the only theoretically important part of the ski jump is the flat face at the tall end (as that's what hits the metal stop and defines where 'closed' is), in practice, if you tried to make it with just a thin wall of plastic sticking up there, it would probably get pushed right over. It needs more material behind it backing it up.

And the extra material behind it has to be ramp-shaped, as the full travel of the valve is more than one full revolution of the rotor. In its first full revolution opening the valve, that ramp has to clear the metal stop—which is being pushed away according to the pitch of the threads as the rotor turns, so the sloping shape of the ski jump makes sure it can clear.

Like a lot of motors in a Prius, the rotor is permanently magnetized. (There's one on my desk at the moment, with a rutted ski jump, and some random metal objects stuck to it.) The only electromagnets are the four stationary coils molded into the stator.

 

@ChapmanF that makes total sense, thank you for clarifying!

 

I was watching a recent South Main Auto episode (YouTube); he’s replacing just a bearing, on a Sienna rear differential (I may not have the precise part name, though it is similar).

Long story a little shorter: he says as far as Toyota is concerned you need to replace the whole component, it’s the “smallest” part no. But he was able to track down the bearing, it did infact have a box, a part no, and so on. They just don’t generally acknowledge its existence or sell it to the public.

perhaps analogous to that EGR valve inverted bucket magnet with ski ramp constituent.