The fluid level in the pump is low.

1. Add power steering fluid, if needed. Refer to Checking and Adding Power Steering Fluid .
2. Inspect the pump for leaks.

The pump belt slips.

Replace the belt. Refer to Drive Belt Replacement in Engine Mechanical - 4.3L or Drive Belt Replacement in Engine Mechanical - 4.8L, 5.3L, 6.0L.

The pump pressure is insufficient.

Refer to Power Steering System Test .