If your vehicle is showing steering wheel is hard to turn or feels heavy, here are the most likely causes and the parts you'll need to fix each one.
The most common reason for heavy steering in hydraulic systems is low fluid. This is usually caused by a leak in the pressure hoses, return lines, or the steering rack itself.
The belt that drives the power steering pump may be worn, loose, contaminated with oil, or completely broken, resulting in an immediate loss of power assist.
The pump that pressurizes the hydraulic fluid can wear out internally. This leads to weak or no assist at low speeds, often accompanied by a loud whining noise.
Many modern vehicles use electric steering instead of hydraulic. If the EPS motor or its control module fails, the steering will instantly become very heavy and a warning light will illuminate.
If power steering components were recently replaced and the system wasn't properly bled, trapped air bubbles will cause stiff, jerky steering and pump cavitation (whining).
Seized ball joints or strut mounts can create severe physical resistance, making the wheels physically hard to pivot regardless of how well the power steering system is working.
Internal seals in the steering rack can blow out, or the mechanical gearing can bind. This causes a heavy or 'notchy' feeling when turning the wheel, sometimes only in one direction.