Turbo Boost Zero

I've got a bunch of half-written blog posts in the can waiting to be finished and released.  Had a really busy summer, and NOT without it's car and e-bike issues.  I'll get them out eventually.

Wanted to give a play by play of this one.  Yesterday I was driving up the big hill in Randolph in my 2002 VW Golf TDI, and my turbo boost went out.  I tried stopping/restarting the car (which has worked in the few times in the past) but... nothing at all.  So whatever is is pretty shot.  As far as I can tell, the car has absolutely no turbo boost at all (I can hear no whistling and feel very little power).  The car is technically drive-able but has a hard time keeping up with traffic.  Reminds me of my old '81 diesel rabbit (NA).

I pulled the codes when I got home, and (among the massive list of other known issues) I saw a new one:

17964 - Charge Pressure Control
            P1556 - 35-00 - Negative Deviation

So at this point I'm thinking that it's one of the following:

• Boost leak (unlikely, since I probably would have heard it)
• Problem with the VNT actuator (misadjusted or stuck)
• Vacuum leak (due to a worn out hose)
• Bad N75 solenoid (this is the interface between the computer and the vacuum)

Stay tuned as I reduce the haystack down to a more manageable size, in search of the needle causing this problem.