21

10 bar
145 psi

Energy outlet service
brake circuit front

22

10 bar
145 psi

Energy outlet service
brake circuit rear

23

8.5 bar
123 psi

Energy outlet clutch
and gearbox switch

25

10 bar
145 psi

Energy outlet
air suspension

26

8.5 bar
123 psi

Energy outlet
auxiliary devices

28.1

8.5 bar
123 psi

Tractor spring brakes

28.2

8.5 bar
123 psi

Tractor spring brakes

28.3

8.5 bar
123 psi

Tractor spring brakes

29.3

8.5 bar
123 psi

Trailer supply

DESCRIPTION

Table 3 – Maximum Circuit Pressures

System Functions
•

External Charge: The external charge function allows
the pressurization of the system – while the vehicle
stationary – through Port 12 on the air dryer without
the need of software control.

•

Heater Management: The heater helps ensure proper
unloader operation under cold conditions by heating
the unloader valve seat, thereby helping prevent
potential freezing. The heater is switched on based on
ambient temperature information broadcast from the
vehicle. In Continuous Flow (CFL) applications, only
one (1) heater will be switched on at a time.

•

Factory Mode: Factory mode is set on non-OEM level
service replacement core modules. The core module
will need to be programmed by an authorized dealer
prior to use. While in factory mode, some features will
be disabled and a warning lamp will be present. The
vehicle should not be driven.

•

Compressor Monitoring: Compressor monitoring
estimates the amount of delivered air by the compressor
(not the air quality). The Bendix® GSAT® system will
also register the number of charge cycles, total charge
time, and the estimated air intake volume to the GSAT
system.

•

CFL Application: For vehicles with a high level of
air consumption, CFL applications can be used. The
CFL application ensures a continuous air volume to
the system (when required). The concept of the CFL
applications utilizes two (2) independent air dryers. The
system can be in charge state with one (1) air dryer and
the second air dryer can be in the regeneration state.

•

Circuit Protection: The function of the Multi-Circuit
Protection Valves (MCPVs) is to protect each reservoir
from pressure loss in the other reservoir, or a pressure
loss in an air accessory. Each of the protection valves
may have different pressure settings. These are
factory-set and must not be changed or adjusted. The
pressure protection valves are non-serviceable.

•

Pressure Limitation: The pressure limitation valve has
a pre-set value for pressure-sensitive circuits. In order
to protect pressure-sensitive systems downstream, the
GSAT system provides a pressure limitation for select
delivery circuits. Standard pressure settings can be
found in Table 3.

•

Compressor Discharge Exhaust (CPE): After the
engine has been switched off, the CPE function is
performed during the self-shutdown process. Due to
the CPE, the air in the compressor discharge line and
cartridge.

•

Engine Start Help (ESH): During engine start (ignition
state), the system charges the compressor control line
to reduce the load to the starter and therefore to the
battery. Function will only be executed if the system
pressure is above a dedicated threshold.

•

Overrun Mode (OVR): To help conserve energy, the
GSAT system uses overrun phases to charge the
reservoirs, meaning the compressor is switched on
when the vehicle is driving downhill so that energy
from the engine is not needed to drive the compressor.
The GSAT system detects an overrun situation from
different vehicle and engine parameters like engine
load, vehicle speed and clutch pedal position. To
utilize these overrun situations in the best way, when
pressurized air is available without engine energy being
consumed, the maximum allowed pressure level in the
reservoirs is increased to the overrun cut-off, so that
even more air can be stored in the reservoirs. During
overrun mode situation the compressor may cut-in at
a higher-than-usual pressure.

•

Overtake Mode (OVT): To decrease the engine load
during high-engine-torque-demanding situations, the
GSAT system switches to OVT. This function is initiated
based on the signal from VMCU, indicating high engine
torque level being over a threshold. In case of an OVT
situation, dedicated cut-in and cut-off thresholds will
be set.

7

System Functions
TRACTOR FUNCTIONS:
•

Manual Truck Parking Brake Apply: Based on the
driver demand via the Hand Control Unit (HCU) (yellow
switch), purge Ports 28.X (tractor) and Port 29.3 to
manually park the vehicle. The pressure decrease in
Port 28.X leads to an increase of the spring brake force
at the wheel ends.

•

External Truck Parking Brake Apply: This function
provides an external interface to the parking brake
system. Parking brakes may be requested by other
systems via CAN. One example of this could be the
service brakes requesting either a partial or full spring
brake application depending on vehicle conditions.

•

Diagnostic Truck Parking Brake Apply: This feature
is available only through a diagnostic tool interface.
It is intended as a diagnostic function to allow a tool
to remotely park the vehicle. Refer to the service tool
instructions for usage and restrictions.

•

Manual Truck Parking Brake Release: Using the
HCU (yellow switch), driver demand will supply Port
28.X to the predefined parking brake supply pressure.
The pressure increase for Port 28.X leads to a decrease
in the spring brake force at the wheel ends.

•

Automatic Truck Parking Brake Release: This is a
comfort function that allows the driver to release the
parking brakes automatically, without HCU actuation,
by recognizing the driver’s intention to take off from
a parked state. The function is initiated by putting
the transmission into drive while the vehicle is still
parked. During the procedure, the spring brakes may
be partially released and then become fully released
when the driver requests throttle. This function works
in conjunction with the service brake system.

•

External Truck Parking Brake Release: This
function is an external request to supply Port 28.X to
the predefined parking brake supply pressure. The
pressure increase for Port 28.X leads to a decrease
in the spring brake force at the wheel ends.

•

Signal Providing Parking Lamp Indication: Based
on the measured pressure in the spring brake ports,
the Bendix® GSAT® system will drive the parking lamp
on the vehicle dash.

8

•

Electronic Anti-compound Parking Brake at
Standstill: To help prevent damage to the wheel
end brakes, the electronic anti-compound function
is utilized to protect the pads/shoes of the disc/drum
brake from too-high forces. In a parked vehicle, the
pads/shoes may have to deal with the spring brake
force of the exhausted spring brake chamber. If the
service brake is applied while the vehicle is parked,
the additional force from the service brake chamber
can lead to overstress at the pads/shoes and must be
prevented. By providing the measured pressure at Port
28.X, the brake controller can adapt the pressure in
the service brake chamber to help avoid a compound
situation at the disc/drum brake while in a standstill
state.

•

Park Request While Vehicle in Motion: This function
activates when the tractor parking brake (yellow switch)
is pulled while the vehicle is in motion above a set
speed threshold and the tractor has been previously
unparked.
here are two (2) possible responses that can result. It
T
is up to the driver to determine the expected response
based on the state of the vehicle when the switch is
pulled.
n a properly operating system, the service brake
O
system of the power unit and trailer will be utilized to
slow the vehicle down. In this case, the service brakes
are only applied when the yellow parking brake switch
is pulled and held in place. Releasing of the switch back
to the neutral position will release the service brakes.
If the switch is held until the vehicle stops, the GSAT
system will transition from a service application to a
parking application by releasing the service brakes and
applying the spring brakes.
If the vehicle is in a faulted state as indicated by the
warning lamps and/or messages in the dash, then
it may be possible that pulling the switch results in
application of the vehicle spring brakes and exhaust
of the trailer supply line if it was previously supplied.
If this occurs, then the tractor spring brake exhaust
and trailer supply line exhaust will latch and will not be
undone when the switch returns to the neutral position.

System Functions
•

Auto Park (Driver Assistance Feature): The Bendix®
GSAT® system’s EPB auto park feature is intended
to help mitigate the possibility of a roll-away resulting
from the driver failing to set the parking brakes of the
vehicle. The EPB on the GSAT system provides the
ability to detect some situations where the vehicle is
in the unparked state and the driver is not present.
In response to a predetermined sequence of inputs,
rollaway mitigation will automatically set the parking
brakes. The rollaway mitigation feature is not intended
to be a primary method to park the vehicle. In all cases,
the driver remains responsible for activating the park
switch for each drive cycle.

Never attempt to test the park request while in motion
feature or use it in the course of normal driving.
This feature is intended for use only in emergency
situations where the tractor and/or trailer service
brakes are not available while driving. Failure to follow
this warning could lead to vehicle damage, property
damage, injury, or death. Drivers and maintenance
personnel must read and understand all GSAT system
operation instructions (available on B2Bendix.com)
before operating a vehicle equipped with a Bendix®
EPB system.

Drivers and maintenance personnel must not rely on
the EPB on the GSAT system to automatically park the
vehicle. Drivers continue to be responsible for safe and
proper operation of the vehicle.
•

Power Unit Parking Brake Release Interlock (Driver
Assistance Feature): The EPB on the GSAT system
provides the ability to restrict the release of the parking
brakes based on inputs from the vehicle, including the
cab doors, service brakes, and ignition switch. This
feature is intended to help mitigate the possibility of
unauthorized operation of the vehicle or release of the
parking brakes without a driver in control of the vehicle.
The standard configuration of this feature inhibits the
release of the power unit spring brakes unless ignition
is “on,” cab doors are closed, and the driver’s foot is
on the service brake.

Drivers and maintenance personnel must read and
understand all GSAT system operation instructions
(available on B2Bendix.com) before operating a vehicle
equipped with a Bendix EPB system.

Activation of the parking brakes while driving should
only be performed by qualified drivers in emergency
situations where the safest action available to the
driver is to activate the parking brakes while driving.
Activation of the parking brakes while driving can
cause a degradation of vehicle control, resulting in
property damage, serious injuries, or death.
The EPB on the GSAT system is designed such that
a short delay is programmed into the park request
while in motion feature. This helps to protect against
accidental actuations.

9

System Functions
TRAILER FUNCTIONS:

OTHER EPB FUNCTIONS:

•

Manual Exhaust of Trailer Supply Line: Based on the
driver demand via the HCU, exhaust trailer Port 29.3.

•

•

Automatic Exhaust of Trailer Supply Line: If
automatic tractor park is activated, then trailer Port
29.3 is exhausted automatically. This is also the trailer
emergency brake function if activated while the vehicle
is in motion.

Pre-trip Function: If the pressure at Primary (Port 22,
rear axle) and Secondary (Port 21, front axle) circuits
are at a predefined pressure threshold, then the trailer
supply (Port 29.3) and tractor spring brakes (Port 28.X)
should be exhausted.

•

Workshop Mode (Disabling of Automatic Parking
Brake Activation): For workshop maintenance
purposes, the automatic parking brake function can
be disabled by shop maintenance. The purpose of
this function is to prevent any unwanted park or trailer
supply actions while the vehicle is in the workshop
environment. Refer to the section titled Special Modes
of Operation in this document for additional details.

•

Rescue: The GSAT system provides two (2) ports to
enable the release of the tractor spring brakes and
the pressurization of the trailer supply line without
electricity. Port 4.3 can be used to supply air to release
the tractor spring brakes. Port 4.4 can be used to
supply air to the trailer red line.

•

Diagnostic Exhaust of Trailer Supply Line: This
feature is available only through a diagnostic tool
interface and is intended as a diagnostic function to
allow a tool to remotely exhaust the trailer supply.
Refer to the service tool instructions for usage and
restrictions.

•

Manual Pressurization of Trailer Supply Line:
»

•

tatic: This function is intended to supply air to
S
the trailer red line via the HCU. There may be an
interlock present that could prevent successful
supply of the trailer, which may be the brake or
accelerator pedal position.

Automatic Pressurization of Trailer Supply Line:
Automatic truck parking brake release may trigger a
“trailer presence test,” which could result in the vehicle
requesting the supply of the trailer.

•

Trailer Presence: The Bendix® GSAT® system may
perform a “trailer presence test” upon request from the
vehicle, which could be used to determine if a trailer
is present or not. Functions that could trigger this test
include manual unpark or supply request, stepping on
the brake pedal while parked, or other functions.

•

Trailer Supply Line Pressure Status Indication:
Based on the measured pressure in the trailer supply
port, the GSAT system will drive the trailer supply lamp
on the vehicle dash.

10

If the rescue function is to be used, refer to OEM
recommendations for proper procedures.

Operation Modes
SPECIAL MODES OF OPERATION
•

he GSAT system will exit the vehicle maintenance
T
mode when any of the following conditions are met.

Vehicle Maintenance Mode (Workshop Mode):
Vehicle maintenance mode allows maintenance or
service personnel to ensure that the Bendix® GSAT®
system will not change from its current state and all
advanced features will be disabled (e.g.: rollaway
mitigation, trailer air charge assist, etc.). Vehicle
maintenance mode is only intended for use when the
vehicle is in a controlled workshop environment and
has been secured from rolling.
nce the GSAT system has entered vehicle
O
maintenance mode, it will remain in its current state
regardless of switch input. For example, if the GSAT
system is in the unparked state and the EPB is placed
into the vehicle maintenance mode, the GSAT system’s
EPB will remain in the unparked state.
efore using vehicle maintenance mode, the wheels
B
must be chocked to ensure the system will not change
state (unparked to parked).
he GSAT system provides two (2) methods to enter
T
into vehicle maintenance mode:
1. A diagnostic service tool (such as Bendix® ACom®
Diagnostic Software); detailed instructions can be
found within the tool.
2. Execution of a predefined sequence of inputs
which are intended to prevent accidental entry into
vehicle maintenance mode.

•

»

he vehicle is driven above a set threshold,
T
typically above 20 mph;

»

Com Diagnostic Software is used to send a
A
command to the GSAT system to exit vehicle
maintenance mode;

»

erform a manual parking brake application by
P
pulling the yellow parking switch;

»