The powersteering pump, which provides the hydraulic pressure to run both the powersteering and the hydraboost hydraulic brake booster, can snap its shaft. The pulley on the pump looks fine, the shaft turns, but INSIDE the pump that thick shaft NECKS DOWN to a (too small!) section, which can snap.

You can tell by trying to pry the powersteering pulley outward, if you can move it in and out an inch or whatever, then you snapped that shaft.

I did it when I was laying on the brakes for all I was worth once; then noticed the steering and brakes were super hard to use. Ended up buying a new pump from DMaxAlliTech and having it replaced by a local shop (cheaper than GM and I didn't want to do it this time).

If you weren't using brakes etc HARD, probably a stuck valve...but try to pry out the pulley, if it is broken you can do it with a medium size screwdriver pretty easy, it doesn't take a crowbar or anything.

GM NEEDS to REDESIGN that pump shaft, I can't BELIEVE this isn't a safety recall issue!!! That thing should NEVER break, if it is so close to design limits just by laying on the brakes, that is DANGEROUS in my opinion.