The fluid level in the pump is low.

Add power steering fluid, if needed.

Refer to Checking and Adding Power Steering Fluid.

The pump belt slips.

Refer to Drive Belt Replacement in Engine Mechanical - 2.4L.

Internal leakage in the steering gear or the pump is high.

Refer to Power Steering System Test Procedure.

The flow control valve sticks closed.

Refer to Power Steering System Test Procedure.