Air Brake System
Brake System General Information
A dual air brake system consists of two independent
air systems that use a single set of brake controls.
Each system has its own reservoirs, plumbing, and
brake chambers. The primary system operates the
service brakes on the rear axle; the secondary sys-
tem operates the service brakes on the front axle.
Service brake signals from both systems are sent to
the trailer.
WARNING
Do not operate the vehicle with the front brakes
backed off or disconnected. Backing off or dis-
connecting the front brakes will not improve ve-
hicle handling and may lead to loss of vehicle
control, resulting in property damage or personal
injury.
If air pressure drops below approximately 70 psi (483
kPa) in either system, a warning light illuminates and
the driver display shows a warning. An audible alert
also sounds if the park brake is not set. See
Table 15.1.
If the low air pressure warning is activated, check the
air pressure gauges to determine which system has
low air pressure. Although the vehicle’s speed can be
reduced using the foot brake control pedal, either the
front or rear service brakes will not be operating at
full capacity, causing a longer stopping distance.
Bring the vehicle to a safe stop and have the air sys-
tem repaired before continuing.
NOTE: The buzzer sounds only when the park
brake is released.
Brake System Warnings, Indicators, and Messages
Telltale Color Description Driver Display
Red
Low Air Pressure
(EPA10 and
Newer)
Indicates air pressure in the primary or
secondary reservoir has dropped below
approximately 70 psi (483 kPa).
f61142906/30/2016
PARK
P
Red
Parking Brake
(EPA10 and
Newer)
Indicates the parking brake is engaged. N/A
Amber Vehicle ABS
Momentary illumination indicates the vehicle
ABS is engaged.
Solid illumination indicates a problem with the
vehicle ABS. Repair the ABS immediately to
ensure full braking capability.
N/A
Amber Trailer ABS
Momentary illumination indicates the trailer
ABS is engaged.
Solid illumination indicates a problem with the
trailer ABS. Repair the ABS immediately to
ensure full braking capability.
N/A
Amber Stability Event
Flashing indicates a stability event has been
detected, and the ESC system is active. Solid
illumination indicates a problem with the
stability system. Repair the ESC system
immediately to ensure full stability capability.
For more information on the ESC system, see
Chapter 7.
N/A
Brake Systems
15.1
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