When they fail, how do they fail?
Its a pulse modulated solenoid. So it opens and closes like a fuel injector to get the right boost characteristics throughout the entire rpm range. No air is lost in these systems.
They tend to fail with the red and blue open (no boost) but most are replaced far ahead of failure time as the response is lowered with the age of the solenoid components. It has been common, to maintain peak performance, to replace the TCV and boost pressure sensor at about 60 K miles. Many of them continue to perform great far after 60K. When Volvo started with actual boost pressure sensors the first design would often go bad by 60K miles.
The turbo control valve (TCV) on my T5-R
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