For adequate operation and lasting service of your power steering system, steering fluid temperature should be kept at certain temperature range. If it overheats, the whole steering system may fail, which leads to quite costly repair. It is the power steering oil cooler, which is responsible for adequate temperature in the system. Usually you will find this guy mounted to the radiator support, mated with the power steering pump by means of lines. If you see a steering error on your dash and your mechanic tells you to replace the cooler, you really should do that to avoid even more serious consequences.