GMC 2003 GMT560 T-Series, Owner'S Manual, Page: 57 / 284

Air Brake
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CAUTION:
When the yellow SYSTEM PARK and the red
TRAILER AIR SUPPLY knobs are both pushed
in, your rig will be free to move. It could strike
someone or something. When both of these
knobs are pushed in, hold the regular brake
pedal down to keep your rig from moving.
If your vehicle has air brakes, you may have these
controls.
Pulling the system park (yellow) knob out applies the
parking brake. The park brake light will not come
on when the air parking brake is applied.
Vehicles built for use as tractors or towing vehicles may
also have the trailer air supply (red) knob.
To charge a trailer’s air brake system do the following:
1. Move your tractor into the proper position.
2. Apply the parking brake by pulling the system park
(yellow) knob out.
3. Hook up the trailer air system properly.
4. Get into the tractor.
5. Push and hold down the regular brake pedal.
6. Push in both the system park (yellow) and the trailer
air supply (red) knobs. This will charge your trailer’s
air system.
After a few minutes, the trailer system should be fully
charged. When it is, the air pressure gage will show
about 125 to 135 psi (862 to 931 kPa).
Yellow Red
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