[pgfpro]

Originally Posted by Christ

It's either boost or engine speed referenced. If there's an actuator on it, it's to control the variable vanes of the compressor turbine.

If you take one of the compressor housings off, you'll see that (probably after a good cleaning, if they're not already clean) the vanes of the compressor wheel move back and forth, effectively changing the angle of attack for the compressor wheel, which changes the pressure/speed ratio of the compressor wheel.

I know how they work... but not HOW THEY WORK. Ya know?

CORRECTION:
It's not the compressor wheel that has movable vanes, it's the inlet geometry that is affected by the solenoid. The throat diameter changes to keep the turbo from over speeding or over boosting. There are a series of ranges that can be manually actuated that will allow for steady boost with increasing compressor speed, or allow for steady compressor speed with changes in boost.

That's kinda what I thought. They look like these... if my memory serves me right.TurboByGarrett.com - GM Duramax (2004.5 - 2009)