The pressure plate is not flat against the cam ring.

Replace the power steering pump. Refer to Power Steering Pump Replacement .

The cam ring is extremely worn.

Replace the power steering pump. Refer to Power Steering Pump Replacement .

The pressure plate, thrust plate, or rotor is scored.

Replace the power steering pump. Refer to Power Steering Pump Replacement .

The vanes are sticking in the rotor slots.

Replace the power steering pump. Refer to Power Steering Pump Replacement .

The vanes are not installed properly.

Replace the power steering pump. Refer to Power Steering Pump Replacement .

There is air in the power steering fluid.

1. Locate and repair the leak. Refer to External Leakage Check .
2. Bleed the power steering system. Refer to Power Steering System Bleeding .

The power steering fluid level is low.

Check and add power steering fluid, if necessary. Refer to Checking and Adding Power Steering Fluid .

The pump belt is slipping.

Inspect the drive belt for wear. Refer to Drive Belt Replacement in Engine Mechanical.