worn steering rack: If the steering rack is worn, it can cause the steering wheel to become stiff when turning to one side or the other.
leaky power steering hose: A leaky power steering hose can cause air to enter the system, leading to stiff steering.
damaged power steering pump: If the power steering pump is damaged, it may not be able to generate enough pressure to properly assist with steering.
electrical problems: In some cases, electrical problems, such as a faulty sensor or relay, can cause the power steering system to malfunction and become stiff.