If your vehicle is showing loud whining noise when turning the steering wheel, here are the most likely causes and the parts you'll need to fix each one.
The most common cause of a steering whine is low fluid, which allows air to enter the pump and cause cavitation. This is usually due to a leak in the aging pressure or return hoses.
If a power steering component was recently replaced or the fluid ran completely dry, trapped air bubbles will cause the pump to whine loudly until the system is properly bled.
Internal wear to the power steering pump's bearings or vanes will cause a constant mechanical whine that gets significantly louder under the load of turning the wheel.
A worn serpentine belt or a weak tensioner can slip under the heavy load of the power steering pump when turning, creating a high-pitched whine or squeal.
Many power steering reservoirs have a built-in, non-removable filter screen at the bottom. If it clogs with debris, it starves the pump of fluid, causing it to whine even if the fluid level appears full.
In rare cases, internal seals inside the steering rack can fail and cause fluid bypass. This leads to pressure fluctuations that make the pump work harder and whine.