GMC 2003 C4C042, Owner'S Manual, Page: 169 / 386

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Air Pressure Gage (If Equipped)
If your vehicle has air
brakes, the air pressure gage
is located above the
switchbank in the center of
the instrument panel.
This gage shows the air pressure for both your front and
rear brake systems.
If the needle on the gage indicates that the air pressure is
below 60 to 75 psi (415 to 517 kPa), the low air warning
light will come on. An alarm will also sound if this
happens.
The yellow pointer shows the pressure available for the
front system, while the green pointer shows pressure for
the rear. There should be no more than 4 psi (28 kPa)
difference showing between the systems.
Don’t drive until both pointers are showing at least
115 psi (793 kPa), so you’ll have enough air if you
need to apply your brakes.
Air Filter Restriction Indicator (Option)
This optional gage is
located above the
switchbank in the center
of the instrument panel.
It monitors the engine
air filter.
As the filter gets dirty, the yellow indicator will begin to
rise. When it reaches 25 inches of vacuum on the scale,
the filter should be replaced.
After replacing the filter, reset the gage by pressing in
the yellow reset button at the bottom of the gage.
If you have a diesel engine, also see your Caterpillar
R
Operation & Maintenance Manual.