GMC Yukon Denali 2013 Owner's Manual page 406

11-6 Service and Maintenance
Footnotes Maintenance
Schedule Additional Required
Services Normal
(1) Check all fuel and vapor lines
and hoses for proper hook-up,
routing, and condition. Check that
the purge valve, if the vehicle has
one, works properly. Replace as
needed.
(2) Or every four years, whichever
comes first.
(3) Do not directly power wash the
transfer case output seals. High
pressure water can overcome the
seals and contaminate the transfer
case fluid. Contaminated fluid will
decrease the life of the transfer
case and should be replaced.
(4) Or every five years, whichever
comes first. See Cooling System on
page 10 14.
(5) Or every 10 years, whichever
comes first.
(6) Inspect for fraying, excessive
cracking, or damage; replace,
if needed.