GMC 2001 Sierra 1500 Pickup Owner's Manual page 133

It is recommended to use this system as follows:
D
For optimum ride comfort in an unloaded vehicle the
button should be out and the indicator light will not
be illuminated. This switch position indicates
NORMAL levels of ride control or damping.
D
For optimum ride comfort when trailering, fully
-
loaded, driving off road, or when personal
preferences demand more control the button should
be pressed in with the indicator light illuminated.
This switch position indicates FIRM levels of ride
control or damping.
The following guide can also be used to help determine
the best setting.
NORMAL: The indicator light will be off when the
system is in this setting. Use for normal city and
highway driving. Provides a smooth, soft ride when
the vehicle is unloaded.
2-50
FIRM (Unloaded): Press the switch to activate this
setting, the indicator light will illuminate. Use this
setting when road conditions or personal preference
demand more control. Provides more "feel" or response
to the road conditions.
FIRM (Loaded): Press the switch to activate this
setting, the indicator light will illuminate. Use this
setting to minimize trailer inputs to the vehicle or
when the vehicle is fully loaded. This setting is also
-
appropriate for off road driving.
You can select a setting at any time based on road
and trailering conditions to provide the best ride and
handling. Select a new setting whenever driving
conditions change.