* Worn power steering pump: This is a common culprit. The pump's internal components wear down over time, leading to increased friction and the characteristic whine, especially under load (turning the wheel). A full fluid level doesn't prevent this internal wear.
* Low-quality power steering fluid: Using the wrong type or low-quality fluid increases friction within the pump and the system's components, leading to noise. Even if the reservoir is full, the fluid itself might be degraded.
* Worn power steering belt: A slipping or worn serpentine belt (which often drives the power steering pump) can cause a whine, particularly at higher RPMs. This isn't directly related to fluid level, but a slipping belt can eventually lead to pump damage.
* Leaks within the power steering system: While the reservoir might appear full, a leak elsewhere in the system (hoses, seals, rack and pinion) can reduce pressure, causing the pump to work harder and whine.
* Worn power steering rack and pinion: The rack and pinion gear assembly can wear down, creating friction and noise. Again, this is independent of the fluid level in the reservoir.
* Air in the system: Even if the reservoir is full, there could still be air trapped in the system. This can cause the pump to work inefficiently and create noise.
In short, the whine is a symptom, not a diagnosis. A full fluid level simply rules out the most obvious (and easiest to fix) problem—low fluid. You need a mechanic to diagnose the underlying cause of the whine.
