A squeaking sound that happens when the steering wheel is turned is likely to be something faulty in the power steering system. However, if the squeaking sounds like it is coming from the front end of the car rather than directly from the steering wheel, it could be related to the suspension. A third possibility for a squeaking sound is loose steering linkage.
If the squeaking sound is coming from the front of the car, it will be fairly faint and possibly accompanied by creaking or clicking. The car performance will also be negatively affected with wandering or vibrations. It usually means that suspension components such as ball joints or bushings are worn.
If the squeaking sound is coming directly from the steering column, it may also sound like a squeal or a whine. This could indicate low levels of power steering fluid, a loose belt or a bad pump. Small leaks are fairly common in power steering systems. They are usually slow leaks, and as the fluid gets low, the steering wheel may start to squeak. This might also be accompanied by a steering wheel that is harder to turn but is easily fixed by topping off fluid when it is low.