Not sure, but I'm guessing it's just a valve that opens and closes.
Here's a summary of the testing procedure in the FSM for the VSV (get out your ohmmeter):
Disconnect both hoses.
A. Inspect for open circuit (continuity)
B. Inspect for ground
C. Inspect for operation... air flows from pipe G (horizontal pipe) to pipe E (vertical pipe). Apply voltage across terminals and check that air does not flow from pipe G to pipe E.
If operation not as specified, replace VSV.
If your CEL is intermittent, it may be that the testing procedure does not produce failing results. The procedure above is just a summary, I recommend getting the FSM so you have everything you need to diagnose. You can subscribe and download the entire FSM and more from techinfo.toyota.com. If I recall the subscription is like $10 for a day.... need a little time and computer space if you're going download a lot, cause all the sections are individual files.
Thanks....This helps! The CEL is pretty consistent. I have to drive 5-10 miles after warm-up, but the CEL (P0401) comes on every time and does not go away until I reset it with my code reader. I will have to take a closer look at the VSV. If I recall correctly, pipe G(horizontal) is the one that goes to the EGR valve, and pipe E (Vertical) loops up and hooks to the bottom of the intake? That is what confused me....it would seem if there is no voltage applied, it would open the valve which would create passage from the underside of the intake to the EGR...but I could be wrong... I have no other symptoms (no roughness, no pinging, etc). I am thinking about removing the EGR and cleaning real well...could just be restricted flow from 178K miles.
I will definately look into the FSM...I can usually get to the bottom of things with the right information. I enjoy a good challenge, and I am cheap...so throwing parts at it is not my style.