When filling or replacing the fluid of the power steering pump reservoir, use GM power steering fluid, part #1050017 or equivalent.
See Figures 1, 2 and 3
Power steering fluid level should be checked at least twice a year. To prevent possible overfilling, check the fluid level only when the fluid has warmed to operating temperatures and the wheels are turned straight ahead. If the level is low, fill the pump reservoir until the fluid level measures between the COLD and HOT marks on the reservoir dipstick. Low fluid level usually produces a moaning sound as the wheels are turned (especially when standing still or parking) and increases steering wheel effort.