* Power Steering Pump: This is the most common culprit. The pump might be failing internally – the bearings could be worn, the vanes could be damaged, or the pump itself could be seizing up. You might hear whining or groaning noises from the pump if this is the case, especially when turning the steering wheel.
* Power Steering Gearbox (Steering Rack or Gear Box): Internal damage within the steering rack can prevent power assist. This could include worn gears, a damaged input shaft, or a leak internally that you can't see. Unusual noises (knocking, grinding) while steering might indicate this.
* Power Steering Pressure Sensor/Switch: While less common, a faulty pressure sensor could prevent the system from functioning correctly. This sensor tells the pump when to engage.
* Low Pressure in the System (despite full fluid): Air in the system can cause a loss of power assist. Even though the reservoir is full, air trapped in the lines or pump can prevent proper pressure buildup. A properly bled system is crucial.
* Belt Issues: A worn, loose, or broken serpentine belt won't drive the power steering pump, resulting in no power steering. Check the belt's condition and tension.
* Fuse or Wiring: Although less likely, a blown fuse or damaged wiring to the pump could also be to blame.
Troubleshooting Steps:
1. Listen for Noises: Pay close attention to any whining, groaning, knocking, or grinding noises while turning the wheel. These sounds often pinpoint the failing component.
2. Check the Belt: Visually inspect the serpentine belt for wear, cracks, or slippage. Make sure it's properly tensioned.
3. Inspect the Pump: Look for any leaks around the pump itself. While you can't directly check the internals easily, unusual noises point to a failing pump.
4. Check the Fluid Level (Again): Make absolutely sure the fluid level is correct and that the fluid isn't burnt (dark brown or black).
5. Professional Diagnosis: If you're not comfortable inspecting the system yourself, a mechanic can perform a more thorough inspection, including pressure testing the system to identify the problem.
Without further information like noises or specific symptoms, it's difficult to pinpoint the exact cause. However, the power steering pump is usually the most frequent suspect when fluid levels are okay.
