Why does the steering wheel in my Renault Trafic pulsate when turning?

A pulsation felt through the steering wheel while turning, as though the power assistance is operating in waves, points to a fault in the power-steering system on a Renault Trafic rather than the suspension. The most common cause is a worn power-steering pump that cannot maintain steady pressure. The pulses can even be felt in the return hose. Before replacing the pump, check two less expensive possibilities: the fluid level and condition, because dark, foamy fluid and an old reservoir strainer can produce identical symptoms, and air trapped in the system. After any work on the hoses, bleed the system by turning the steering wheel from lock to lock with the front of the vehicle raised. If the pulsation is accompanied by a whine that becomes louder when turning at a standstill, the pump is already badly worn and needs replacing.