SD-24-250V
Bendix® GSAT® (Global Scalable Air Treatment) System for Volvo® Trucks
INTRODUCTION
The Bendix ® GSAT® (Global Scalable Air Treatment)
system is an intelligent air-processing system designed
to collect and remove air system contaminates in solid,
liquid, and aerosol form before they enter the brake system.
Combined with an Electronic Parking Brake (EPB) module,
the GSAT system provides air treatment, distribution, and
parking capability for commercial vehicles that utilize air
brakes. GSAT is available in various models to support a
wide range of applications.
The Air Processing Module 3 (hereinafter referred to as the
GSAT system) is a variant of the GSAT system for Volvo®
trucks. The GSAT system adds intelligent Electronic Air
Control (EAC) for the air compressor. The system also
provides the basic governor operation to maintain safe
air pressure levels, air system diagnostic and prognostic
information, and additional features. The GSAT system
integrates advanced functions to optimize air system
pressure control and conserve energy. Additionally, the
system module has advanced regeneration operations to
protect the air system against moisture ingress.
The GSAT system communicates on the vehicle CAN bus
and receives vehicle information including engine speed,
torque, and other vehicle operational conditions. The GSAT
system also transmits compressor state and diagnostic
and prognostic information, including cartridge lifetime
prediction on the vehicle CAN bus.
GSAT functionally replaces conventional Bendix ®
air treatment products and integrates parking brake
management capabilities. With the inclusion of an
electronic controller and electromechanical relay valves,
the GSAT system provides many of the same features
and functions as manual parking brake valves, but also
provides advanced features and functions not available in
the previous parking brake valves.

Improper use of the EPB system can result in an
unsafe park state, causing property damage, serious
injuries, or death. Drivers must always be responsible
for the safe operation of the vehicle at all times. The
EPB system does not replace the need for a skilled
driver, reacting appropriately and in a timely manner,
and using safe driving practices. If the EPB system
is faulted, or if for any reason the vehicle operator
believes the parking system did not properly park
the vehicle, then the vehicle operator is responsible
for executing a backup parking action; this includes
turning off the engine and pumping the foot brake valve
until all air is depleted from the service reservoirs (also
known as fanning down the reservoirs).

The EPB system cannot detect issues with other
components of the parking brake system, such as
the spring brake chambers. Drivers and maintenance
personnel must perform inspections and maintenance
on the parking brake system in accordance with
established procedures. For proper operation of the
EPB system, all other components of the parking brake
system must be functioning as designed.

Figure 1 – GSAT System

1

GENERAL SAFETY GUIDELINES

WARNING! PLEASE READ AND FOLLOW THESE INSTRUCTIONS
TO AVOID PERSONAL INJURY OR DEATH:

When working on or around a vehicle, the following guidelines should be observed AT ALL TIMES:
▲ Park the vehicle on a level surface, apply the ▲ Never connect or disconnect a hose or line
parking brakes, and always block the wheels.
containing pressure; it may whip and/or cause
Always wear personal protection equipment.
hazardous airborne dust and dirt particles. Wear
eye protection. Slowly open connections with
▲ Stop the engine and remove the ignition key
care, and verify that no pressure is present. Never
when working under or around the vehicle.
remove a component or plug unless you are
When working in the engine compartment,
certain all system pressure has been depleted.
the engine should be shut off and the ignition
key should be removed. Where circumstances ▲ Use only genuine Bendix ® brand replacement
require that the engine be in operation, EXTREME
parts, components, and kits. Replacement
CAUTION should be used to prevent personal
hardware, tubing, hose, fittings, wiring, etc.
injury resulting from contact with moving,
must be of equivalent size, type, and strength as
rotating, leaking, heated, or electrically charged
original equipment and be designed specifically
components.
for such applications and systems.
▲ Do not attempt to install, remove, disassemble, ▲ Components with stripped threads or damaged
or assemble a component until you have read,
parts should be replaced rather than repaired.
and thoroughly understand, the recommended
Do not attempt repairs requiring machining or
procedures. Use only the proper tools and
welding unless specifically stated and approved
observe all precautions pertaining to use of those
by the vehicle and component manufacturer.
tools.
▲ Prior to returning the vehicle to service, make
▲ If the work is being performed on the vehicle’s
certain all components and systems are restored
air brake system, or any auxiliary pressurized air
to their proper operating condition.
systems, make certain to drain the air pressure ▲ For vehicles with Automatic Traction Control
from all reservoirs before beginning ANY work
(ATC), the ATC function must be disabled (ATC
on the vehicle. If the vehicle is equipped with
indicator lamp should be ON) prior to performing
a Bendix ® AD-IS® air dryer system, a Bendix ®
any vehicle maintenance where one or more
™
®
®
DRM dryer reservoir module, a Bendix AD-9si ,
wheels on a drive axle are lifted off the ground
AD-HF®, or AD-HFi® air dryer, be sure to drain the
and moving.
purge reservoir.
▲ The power MUST be temporarily disconnected
▲ F o l l o w i n g t h e v e h i c l e m a n u f a c t u r e r ’s
from the radar sensor whenever any tests USING
recommended procedures, deactivate the
A DYNAMOMETER are conducted on a vehicle
electrical system in a manner that safely removes
equipped with a Bendix® Wingman® system.
all electrical power from the vehicle.
▲ Never exceed manufacturer’s recommended
pressures.
▲ You should consult the vehicle manufacturer's operating and service manuals, and any related literature,
in conjunction with the Guidelines above.

2

Refer to Table 1 for frequently used acronyms and their
definitions.
ACRONYM

Refer to Table 2 for terms often used interchangeably.

DEFINITION

FREQUENTLY INTERCHANGED TERMS

ABS

Antilock Braking System

Regenerate

Purge

CAN

Controller Area Network

Load

Charge

CFL

Continuous Flow

Inflation

Pressurization

CPE

Compressor Pipe Exhaust

Deflation

Exhaust

CPM

Cartridge Predictive Maintenance

Energy Outlet

Delivery Port

DTC

Diagnostic Trouble Code

Table 2 – Frequently Interchanged Terms

EAC

Electronic Air Control

EBS

Electronic Braking System

ECM

Electronic Control Module

ECU

Electronic Control Unit

EPB

Electronic Parking Brake

ESH

Engine Start Help

GSAT

Global Scalable Air Treatment

HCU

Hand Control Unit

MCPV

Multi-Circuit Protection Valve

MCU

Microcontroller Unit

OEM

Original Equipment Manufacturer

OVR

Overrun Mode

OVT

Overtake Mode

pHMI

Peripheral Human Machine Interface

PVM

Park Valve Module

TCM

Trailer Control Module

TMC

Truck Maintenance Council

XPR

External Park Request

IMPORTANT
Bendix®-brand Electronic Control Units (ECUs) are
not designed to store data for purposes of accident
reconstruction, and Bendix ® ACom ® Diagnostic
Software is not intended to retrieve data for purposes
of accident reconstruction. Bendix makes no
representations as to the accuracy of data or video
retrieved and interpreted from ECUs for purposes
of accident reconstruction. Bendix does not offer
accident reconstruction services or interpretation of
stored data. Bendix ECUs are not protected from fire,
loss of power, impact damage, or other conditions that
may be sustained in a crash situation and may cause
data to be unavailable or irretrievable.

Table 1 – Acronyms

3

System Components

SYSTEM COMPONENTS
Advanced functions of the Bendix® GSAT® system allow
management of the tractor parking brakes and provide trailer
air supply. The modularity of the GSAT air management
system provides scalability.

The core module is comprised of three (3) sub-modules:
a. M
ulti-Circuit Protection Valve (MCPV) – this
sub-module operates similarly to the valve body
of a Bendix® AD-IS® Air Dryer Module.

See Figure 2. The GSAT system is comprised of two (2)
main components:

b. E
lectronic Parking Brake (EPB) – this submodule contains the pneumatic relay valve(s)
and is controlled by internal solenoids and the
Electronic Control Unit (ECU).

1. Air Dryer
2. Core Module

c. E
lectronic Control Unit (ECU) – the ECU controls
the primary/smart functions of the GSAT system
including EPB and air-processing features.
If replacing the GSAT system, use the same mounting
location – and, if necessary, bracketry – as installed by
the Original Equipment Manufacturer (OEM). The GSAT
system is designed to be secured to a bracket on the
chassis using M12 flange bolts. Refer to Table 4 for torque
specifications.

Multi-Circuit Protection
Valve (MCPV)
Air Dryer

GSAT System
Electronic Parking
Brake (EPB)

Core Module

Electronic Control
Unit (ECU)

Figure 2 – GSAT System Components

4

System Components
1. Air Dyer: The air dryer provides clean, dry air to the
components of the brake system, which increases the
life of the system and reduces maintenance costs. The
air dryer is supplied with an oil-coalescing cartridge.
This cartridge contains a coalescing media at the inlet
of the desiccant bed that provides a higher level of oil
removal over the standard air dryer cartridges.

IMPORTANT
The air dryer must always remain equipped with an oilcoalescing cartridge. Failure to use Genuine Bendix®
oil-coalescing filter cartridges and failure to maintain
cartridges within the recommended intervals can result
in damage to vehicle components or systems.
2. Core Module: The core module is the main hub of
the Bendix® GSAT® system and contains three (3)
sub-modules.

Accumulation of road debris on the GSAT system
may cause blockage of the core module exhaust
ports. If the exhaust ports are blocked or restricted,
parking brake performance will be affected, potentially
resulting in undesirable performance of the parking
brake system. Undesirable performance of the parking
brake system may cause property damage, personal
injury, or death. The core module must be mounted as
described in this document to minimize the possibility
of accumulated debris on the exhaust ports. The
exhaust ports must have a minimum of 1-in. clearance
from all obstructions. The exhaust ports must not be
covered or painted over.

a. M CPV Module: The MCPV is the primary
distribution module for the delivery circuits and
contains pneumatic valving to protect the vehicle air
system in the event of a circuit failure downstream.
The MCPV also contains a pressure limitation
pneumatic valve for use with pressure-sensitive
components.
b. EPB Module: The EPB contains the relay valve
for parking brake control as well as trailer supply.
c. ECU Module: The GSAT system is controlled by
the integrated functionality located within the ECU.
• The ECU monitors the air system pressure. The
unit energizes and de-energizes the solenoids to
control compressor and desiccant regeneration.
• The

ECU receives engine speed, torque, and
vehicle speed from the engine Electronic Control
Module (ECM) to provide advanced features.
• The

ECU controls the parking brake application
of the tractor. Internal solenoids are used to apply
and release the tractor spring brakes.
• The ECU controls the trailer supply. Internal
solenoids are used to supply and exhaust the
trailer system.
•
T he GSAT system uses the dash display
and telltale lamps to advise the driver of any
malfunctions. DTCs can be displayed via Bendix®
ACom® Diagnostic Software to evaluate system
status.

5

System Functions

SYSTEM FUNCTIONS

verpressure warning indication: The pressure
O
at Port 21 (Secondary) and Port 22 (Primary) is
measured and observed by the GSAT system
internally. If the pressure increases above the
high-pressure threshold, a Diagnostic Trouble
Code (DTC) can be triggered.

»

Integration of the Bendix® GSAT® system by the vehicle
OEM provides the following functions:
VEHICLE AIR MANAGEMENT FUNCTIONS
•

Pressure Regulation: The GSAT system provides
basic governor control and loads/unloads the
compressor to maintain a set air system pressure
level. When the air pressure drops below the cut-in
pressure threshold, the GSAT system will load the
compressor; when the air pressure is greater than
the cut-out pressure threshold, the GSAT system will
unload the compressor.

•

Air Compressor Control: This function controls the
compressor by controlling its air output.

•

Compressed Air Processing:
»

»

•

Intermediate regeneration strategy is intended to
be used in case of high air consumption. In case
of intermediate regeneration, the cut-in and cut-out
pressure thresholds are decreased. The purpose
of intermediate regeneration is to avoid cartridge
saturation during high air consumption situations
and long compressor charge cycles. An extra
regeneration cycle is executed interrupting the
charge mode and/or executed on an increased
charge duration.

Signal Broadcasting (Information Providing):
»

»

6

he cartridge regeneration function ensures that
T
the drying capability during charge modes is
adequate. During regeneration, air is pulled from
Port 22 (Primary) and Port 21 (Secondary) in order
to remove moisture from the desiccant cartridge.
The vehicle operator may notice that the system
pressure depletes slightly during regeneration.

Inadequate pressure indication: The pressure at
Port 21 (Secondary), Port 22 (Primary), and Port
29.3 (Trailer Supply) is measured and observed
by the GSAT system internally. If the pressure in
any of the measured ports drops below the set
threshold, the GSAT system provides an indication
lamp request via CAN. If the pressure is below
approximately 100 psi, the GSAT system provides
an indication to the vehicle via CAN and the spring
brakes cannot be released and the vehicle remains
parked.
ow pressure warning indication: The pressure
L
at Port 21 (Secondary) and Port 22 (Primary) is
measured and observed by the GSAT system
internally. If pressure drops below the low-pressure
threshold, the GSAT system provides a warning
lamp request via CAN.

•

Cartridge Predictive Maintenance (CPM): As the
desiccant cartridge ages, the GSAT system reports the
cartridge life remaining and will fault if the cartridge life
falls below predetermined levels. Bendix recommends
following the OEM guidelines for cartridge replacement
which could be when the vehicle reports that it is
needed or if a predetermined time has passed. When
the cartridge is replaced, refer to service action code
F in the troubleshooting section of this document for
instructions on how to reset the cartridge monitor.

•

Air Distribution: Internal valving will allow the
distribution of air in a preferred fill-up sequence and
different pressure levels. This ensures protection of the
system components downstream of the GSAT system.
Standard pressure settings can be found in Table 3.
DELIVERY
PORT

MAXIMUM
CIRCUIT
PRESSURE