Im not sure if always comes up on vagcom,
My car was at VW 6 days before and they said no faults hmm,
At Revo the fault came up and we went for a drive with vagcom hooked up and
he could tell the car was not holding boost.
I was so happy to find the rip in DV, the car was instantly better even before putting the select in.
I think give away signs are hearing the boost leaking,\i have also noticed since i can hear the
DV noise as you come off power,
Hope this helps
Rob