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: