GMC 2003 GMT560 T-Series Owner's Manual page 50

Diesel Engine Exhaust Brake
The exhaust brake is used to help slow the vehicle and
may assist the vehicle's foundation brakes. The use
of the exhaust brake will assist the braking of the vehicle
and prolong the life of the foundation brake lining
material.
Push the bottom of the switch to turn the exhaust brake
on. When you push the top of the switch, the exhaust
brake will turn off.
There is an indicator light on the instrument panel
similar to the symbol on the switch, that will come on
when the exhaust brake is active.
2-14
The exhaust brake switch
is located in the instrument
panel switchbank.
When using the exhaust brake, the proper gear range
selection is important. The exhaust brake will be
most effective if the gear range selected is the lowest
possible range that does not allow the engine rpm to go
more than 200 rpm above rated (full load) rpm. Do
not exceed 2400 rpm.
If you have an automatic transmission and press this
button, the transmission will downshift to a factory
default setting of fourth gear. To change the default
setting, or for more information on factory default
settings, contact your dealer for assistance.
The accelerator and clutch pedals must be released in
order for the exhaust brake to engage. The exhaust
brake will not function when the cruise control feature is
active, and will automatically shut off when the
anti-lock brake system is active.
Two-Speed Rear Axle Electric Shift
Control
If your vehicle has this feature, you'll find a label on the
headliner above the windshield or in another place
near the driver that shows how to use it.