Hummer 2003 H2 Owner's Manual page 238

TC2 only operates in the following transfer case modes:
D
4HI Lock
D
4LO Lock
D
4LO Lock and Differential Lock
It will not operate in 4HI. If the TC2 button is pressed
while in 4HI, the light will flash for about 15 seconds
and then go out. The light should also come on briefly
when you turn the ignition key to RUN; if it doesn't,
see your dealer for service.
4-10
To enter this mode, press
the TC2 button located on
the instrument panel to the
right of the steering wheel.
If you restart your engine, the system reverts to the
TCS mode.
The TRAC OFF light will come on when a Traction
-
Control System, Anti Lock Brake System or
-
engine related problem has been detected and the
vehicle needs service. See "TRAC OFF Light" in
the Index.
The Traction Control System, as delivered from the
factory, will automatically come on whenever you start
your vehicle.
When the TRAC OFF light
is on, adjust your driving
accordingly.