Whenever a major component, such as a pump or rack, is replaced, the hydraulic system should be flushed with fresh fluid. This prevents previously circulating contaminants, such as swarf, from shortening the life of the replacement part. Should the reservoir have a filter, it must be clean and unblocked; in some cases, it cannot be cleaned and you will have to replace the reservoir.
Remove the pump’s high-pressure pipe at the steering rack end and place a suitable receptacle on the floor to catch the fluid as you pour it into the reservoir. When the colour of the fluid that runs from the pipe is of the same hue as that poured in, you know that the old, dirty fluid has been purged from that part of the system.
To flush the steering rack, disconnect the return pipe from the rack to the reservoir at the reservoir end. Plug the reservoir connection so that fluid cannot escape and fill the reservoir with fluid. With the front wheels raised and the engine off, turn the steering wheel slowly from lock-tolock, ensuring not only that the displaced fluid is collected but also that the reservoir fluid level does not fall too low, allowing air to be drawn into the system. With the ignition, or fuel, supply disabled (note that this could trigger a fault code on some vehicles), crank the engine over, ensuring that it does not start. This floods the mechanical pump with new fluid. On electro-hydraulic pumps, you may have to start the engine briefly. Reconnect the disconnected pipes and carry out the following bleeding procedure.