Is it necessary to do this and how often should I do it?
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2006 Toyota Corolla Question: power steering fluid change
Answer #1patrick mannion from Greg Solow's Engine Room, April 17, 2009, 11:27Master
Flushing power steering fluid should be done if the fluid is exceptionally discolored, power steering components are changed or steering difficulties are experienced.
As a maintainence item the fluid should be flushed every 30,000 miles for long term durability of steering components but manufacturers generally don't require doing it. Its up to the customer and there long term desires for the car. Generally not seen as a must do service item.