GMC 2004 Sierra - Manual (Page 445)

Power Steering Fluid
When to Check Power Steering Fluid
It is not necessary to regularly check power steering fluid
unless you suspect there is a leak in the system or
you hear an unusual noise. A fluid loss in this system
could indicate a problem. Have the system inspected
and repaired. See
Engine Compartment Overview
on page 5-12 for reservoir location.
8100 V8 Engine
All Other Engines
5-45