If your vehicle is showing power steering warning light stays on, here are the most likely causes and the parts you'll need to fix each one.
Electric power steering (EPS) systems draw a massive amount of electrical current. If your battery is weak or the alternator is failing, the vehicle's computer will disable the power steering to conserve power, triggering the warning light.
If the battery was recently disconnected or replaced, the steering system may lose its center calibration. The warning light will stay on until the system is reset, usually by turning the steering wheel lock-to-lock.
On vehicles with electro-hydraulic steering, a drop in fluid level due to a leak will trigger the warning light to prevent damage to the pump.
The electric motor that provides steering assist can overheat or fail internally over time. This completely disables power steering assist and illuminates the warning light.
A blown fuse or a stuck relay will cut electrical power to the steering module or motor, instantly triggering the warning light and causing heavy steering.
On hydraulic systems, a failed pressure sensor will send incorrect data to the engine computer, turning on the warning light even if the steering feels completely normal.