If your vehicle is showing hissing noise from the steering wheel area when turning, here are the most likely causes and the parts you'll need to fix each one.
Low fluid levels allow air to enter the power steering pump, causing the fluid to aerate. This creates a hissing or whining noise that travels up the steering column when the wheel is turned.
If power steering components were recently replaced or disconnected and the system was not properly bled, trapped air will cause a loud hissing or groaning noise when the steering wheel is turned.
The rotary control valve inside the steering rack directs high-pressure fluid based on steering input. As its internal seals wear out, fluid bypasses the valve, creating a noticeable hissing noise directly behind the steering wheel.
An internally collapsed or degraded power steering pressure hose forces fluid through a restricted opening. This creates a high-pressure hiss that transmits through the steering components into the cabin.
The rubber boot that seals the steering column at the firewall can dry out over time. As the steering shaft turns, it rubs against the dry rubber, creating a friction noise often mistaken for a pneumatic hiss.