* Low Fluid Quality: While the reservoir might be *full*, the fluid itself could be old, contaminated, or low in viscosity. Old power steering fluid breaks down, losing its lubricating properties, leading to whining. The pump is essentially working harder to compensate.
* Worn Pump: The pump itself might be wearing out. Internal components like the vanes or bearings can wear, causing increased friction and the characteristic whine. This is a common cause of power steering pump noise as they age.
* Worn or Damaged Pulley: The pulley that drives the pump can become worn, misaligned, or damaged. This can lead to inconsistent belt tension and inefficient power transfer, causing the pump to whine. Check for cracks or excessive wear.
* Belt Tension: An overly tight or loose serpentine belt can also cause a whine. The pump needs the correct belt tension to operate efficiently. Too loose, and it slips; too tight, and it puts extra strain on the pump and other components.
* Internal Pump Leaks: Even with a full reservoir, internal leaks within the pump can starve it of sufficient fluid under pressure, causing the whine. This is harder to diagnose visually.
* Stuck or Corroded Valves: Internal valves within the pump can become stuck or corroded, hindering smooth fluid flow. This increased resistance can produce the whining sound.
* Power Steering Rack or Gearbox Problems: While less likely to *directly* cause a pump whine, problems in the steering rack or gearbox can put increased load on the pump, contributing to the noise.
Troubleshooting Steps:
1. Check the fluid: Even if the reservoir is full, drain and replace the fluid with fresh, manufacturer-recommended power steering fluid. This is the cheapest and easiest first step.
2. Inspect the belt and pulley: Visually check the serpentine belt for cracks, fraying, or glazing. Also, check the power steering pump pulley for any damage or looseness.
3. Check belt tension: Use a tension gauge or the "thumb press" method (applying firm pressure to the belt midway between pulleys) to ensure proper tension. Consult your owner's manual or a repair manual for specifications.
4. Listen carefully: Try to pinpoint where the whine is coming from. Is it definitely the pump, or could it be another accessory driven by the same belt?
If replacing the fluid and inspecting the belt/pulley doesn't resolve the issue, you'll likely need a professional mechanic to diagnose and repair the power steering pump or other related components. Ignoring a whining power steering pump can lead to complete pump failure, potentially leaving you without power steering.
