Supply Pressure

Foundation
Brakes

GSBC® EPM-90™
Reservoir

Figure 3 – GSBC System Pneumatic Backup Mode Example
Pneumatic Signal

Bendix® EC-80™
ECU

Driver Brake
Demand

Service Brake
Pressure

Brake Control Pressure

Wheel Speed
Sensor
Service Brake
Pressure

Supply Pressure

Foot Brake
Valve

Relay Valve
Reservoir

ABS
Modulator

Foundation
Brakes

Figure 4 – ABS Faulted Operation Example

SD-27-5023V Rev 002 Bendix® GSBC® System and EBS-90™ (Global Scalable Brake Control System and Electronic Control Unit)

7

System Components

SYSTEM COMPONENTS
GSBC is comprised of fewer components than previous
brake control systems. As a result, valves that an
experienced driver or technician may be accustomed
to seeing on a vehicle will not be present, or have been
incorporated into other components.
Refer to Table 1 on page 11 for assistance in locating
components on a vehicle equipped with GSBC.
GSBC CENTRAL ECU (BENDIX® GSBC® EBS-90™)
The GSBC Central ECU is a frame-mounted, ruggedized,
weatherproof Electronic Control Unit (ECU). Unlike previous
Bendix brake control ECUs with Bendix Electronic Stability
Program (ESP), the Central ECU is located on the exterior
of the vehicle on a rigid mount. It is important to ensure that
the mounting location of the Central ECU is rigid as it also
contains the Yaw Rate Sensor (YRS) used by the brake
controller’s ESP function. Loose mounting bolts or flexibility
in the ECU mount can lead to poor system performance,
faults, or unintended or unwanted ESP interventions.

FOOT BRAKE MODULE (BENDIX® GSBC® FBM-40™)
The Foot Brake Module (FBM) provides driver control
over the service brake system. The FBM incorporates
the Foot Brake Valve (FBV) and brake demand sensors
present in previous brake control systems. Pneumatically,
the components are very similar. The FBM is supplied by
both the primary and secondary pneumatic circuits and will
always deliver pressure on both the primary and secondary
circuits in response to driver demand if air is present in the
service reservoirs.
To enable the advanced features and functions offered
by the GSBC system, the FBM will continuously monitor
the position of the brake pedal electronically. If the driver
requests a change in braking force by moving the brake
pedal, the FBM will electronically transmit that information
to the Central ECU so that the system can respond
appropriately.
For more information about the FBM, refer to SD-27-5028,
GSBC FBM Service Data Sheet, on B2Bendix.com.

The Central ECU is parameterized when the vehicle is
built to match the mounting position and orientation on
the vehicle. Under no circumstances can the Central
ECU be relocated, reoriented, or replaced without
consulting the vehicle OEM. For more information about
the Central ECU, refer to page 18 of this document.

The Central ECU in a GSBC system must not be
relocated or reoriented on the vehicle. Relocation or
reorientation of the Central ECU can cause improper
stability control function and potential non-compliance
with regulations.

Figure 5 – GSBC FBM-40
ELECTRO-PNEUMATIC MODULE (BENDIX® GSBC®
EPM-90™)

Bendix ESP is designed and optimized for trucks
and for tractors that tow single trailers. If a tractor
equipped with Bendix ESP is used to tow multiple
trailer combinations (commonly known as “doubles”
or “triples”), the effectiveness of Bendix ESP may be
greatly reduced. Extremely careful driving is always
required when towing multiple trailer combinations.
Excessive speed and aggressive maneuvers – such
as sharp turns, sudden steering inputs, or abrupt lane
changes – should be avoided.

8

The Electro-Pneumatic Modules (EPMs) are electronically
controlled proportional relay valves. They are available in
either one channel (1C) or two channel (2C) variants. In
comparison to previous brake control systems, the EPMs
incorporate the traction control solenoid, relay valve, Hill
Start Assist (HSA) solenoid valve assembly, and, in the
case of the 2C EPM, modulators. Typically, 1C EPMs are
used for steer axles and lift axles, and 2C EPMs are used
for driven axle(s).
NOTE: The GSBC system has a minimum of two (2) and
a maximum of four (4) EPMs per vehicle.

SD-27-5023V Rev 002 Bendix® GSBC® System and EBS-90™ (Global Scalable Brake Control System and Electronic Control Unit)

System Components
EPMs are in constant communication with the Central
ECU by a dedicated brake CAN communications link that
is entirely separate from the other CAN networks on the
vehicle. If the driver requests a change in brake force using
the foot brake pedal, the EPMs will provide the requested
amount of pressure to the wheel ends that they control. If
the Central ECU makes a request for brake pressure (for
example, to perform an ESP, ATC, or HSA intervention) the
EPMs will respond in much the same way.

Never splice, cut, extend, or otherwise disturb a brake
CAN line. There are no diagnosable signals on brake
CAN, and any modification to brake CAN wiring can
result in EBS malfunction, faults, and warnings, up to
and including those that disable required functions
such as ESP and ABS.
On driven axles, the controlling EPM also provides ABS,
ATC, and HSA functionalities. Unlike previous Bendix
brake control systems, GSBC does not require additional
mechanical valves or plumbing to enable these features.
EPMs are also equipped with a backup solenoid, which
will prevent control air pressure supplied by the FBM from
flowing into the EPM if the system is operating normally.
This ensures that the electronic control system manages
the braking effort of the vehicle in most scenarios.
If the system is in Pneumatic Backup Mode, the solenoids
inside the EPMs are not powered, allowing the pneumatic
signal from the FBM to flow into the EPM, which allows the
EPM to operate as a mechanical relay valve.
For more information about EPMs, refer to SD-27-5031,
GSBC EPM Service Data Sheet, on B2Bendix.com.

ELECTRONIC TRAILER PRESSURE CONTROL
MODULE (BENDIX® GSBC® eTPCM-90™)
The Electronic Trailer Pressure Control Module (eTPCM)
is an electronically controlled proportional relay valve. The
eTPCM works with the Bendix® GSAT® (Global Scalable
Air Treatment) system and GSBC system to provide trailer
service brake (blue gladhand) air control as well as trailer
emergency (red gladhand) air. For more information on
GSAT, refer to SD-24-250V, GSAT System Service Data
Sheet, on B2Bendix.com.
Unlike the EPM, the eTPCM does not communicate over
a dedicated brake CAN communications link. Instead, it
is directly connected to the Central ECU which provides
analog control of the eTPCM solenoids.
The eTPCM receives pneumatic control input from both
the primary and the secondary brake circuits via the FBM.
The valve receives supply air from GSAT, which is used to
supply the internal relay valve delivering pressure to trailer
service brake control line, through the blue gladhand. The
supply pressure is also allowed to pass through the valve
to provide the emergency/supply (red) gladhand with air
(when enabled).
When the system is operating in Electronic Primary
Mode, the Central ECU will use the eTPCM solenoids to
electronically control the pressure sent to the trailer service
brake control. Similar to the EPMs, the eTPCM also has
a backup solenoid that prevents pneumatic control air
pressure from flowing from the FBM into the eTPCM relay
valve when the system is operating in Electronic Primary
Mode.
In the event of a critical system failure, the system will fall
back to Pneumatic Backup Mode. In this mode, the backup
solenoid will not close and the solenoids in the eTPCM will
not be activated. As a result, control pressure will flow into
the eTPCM from the FBM, which will operate the eTPCM
as a mechanical relay valve.
For more information about the eTPCM, refer to
SD-27-5036, GSBC eTPCM Service Data Sheet, on
B2Bendix.com.

Figure 6 – GSBC EPM-90 (1C and 2C)

Figure 7 – GSBC eTPCM-90

SD-27-5023V Rev 002 Bendix® GSBC® System and EBS-90™ (Global Scalable Brake Control System and Electronic Control Unit)

9

System Components
MODULATOR (BENDIX® GSBC® M-50QR™)

WHEEL SPEED SENSOR (BENDIX® WS-24™)

The M-50QR modulator is a high-capacity, on/off pneumatic
device that can help provide antilock control for the wheel(s)
it controls. The modulator has both electrical and pneumatic
connections, and is typically located close to the brake
chamber(s) it is controlling. For Volvo vehicles with GSBC,
there are two (2) modulators, located on each side of the
vehicle near the brake chambers on the front axle. Antilock
control for all other axles on the vehicle is provided by the
EPM(s) controlling those axle(s).

Wheel Speed Sensors (WSSs) detect the speed of an
individual wheel end and transmit that information to the
brake control system. The WSS is fixed to the axle of a
vehicle and does not move as the wheel end itself rotates.
The sensor is pointed towards a tone ring that is fixed to the
spinning wheel, and as the wheel spins, the WSS detects
the movement of the tone ring. The WSS turns this sensed
rotational information into an analog signal, which is read
by the EPM. The EPM translates this analog signal into
a digital signal, which is in turn transmitted to the Central
ECU over the brake CAN communications link.

The purpose of the modulator is to prevent the brakes that
it controls from “locking up” or from becoming stationary
while the vehicle is still in motion This is essential to the
operation of the ABS function. More information about the
ABS function and how it works can be found in BW8207,
GSBC System Operator’s Manual, or in Section 6 of
BW5057, Bendix Air Brake Handbook, on B2Bendix.com.
Depending on the situation, the modulator can hold off
application pressure from the wheel end, hold a steady
pressure at a wheel end relative to the pneumatic control
signal, or exhaust the pressure at a wheel end relative
to the pneumatic control signal, all by controlling two (2)
solenoids electronically. The functionality of holding or
decreasing pressure at an individual steer axle wheel end
is a key component of maintaining vehicle stability under
hard braking, or in adverse road or weather conditions.
For more information about the M-50QR modulator, refer
to SD-27-5170, GSBC M-50QR Service Data Sheet, on
B2Bendix.com.

For more information about the WSS, refer to SD-13-4860,
Bendix WS-24 Service Data Sheet, on B2Bendix.com.

Figure 9 – Bendix WS-24 90° and Straight Variants
STEERING ANGLE SENSOR (BENDIX® SAS-80™)
The Steering Angle Sensor (SAS) is an electronic sensor
installed in the steering column. The SAS detects and
transmits the angle to which the driver has turned the
steering wheel over the CAN communications link to the
Central ECU, which uses that information to help improve
the performance of ESP and other advanced functions.
For more information about the SAS, refer to SD-27-4709,
Bendix SAS Service Data Sheet, on B2Bendix.com.

Figure 8 – GSBC M-50QR

Figure 10 – Bendix SAS-80
COMPONENT INSTALLATION/REPLACEMENT
Refer to the component-specific Service Data sheet on
B2Bendix.com for troubleshooting, and installation and
replacement procedures for that particular component.

10

SD-27-5023V Rev 002 Bendix® GSBC® System and EBS-90™ (Global Scalable Brake Control System and Electronic Control Unit)

System Components
COMPONENT LOCATION AND SERVICE DATA SHEET REFERENCE
This information is intended as a general guideline for GSBC system components and the location of components
depending on the specific application the vehicle is built for. Contact the vehicle OEM for more information.
GENERAL LOCATION

FUNCTION

Foot Brake Module (FBM-40)
SD-27-5028

GSBC COMPONENT

Firewall, connected to the brake pedal

Converts driver input into pneumatic and electronic
request for service braking.

Electro-Pneumatic Module
(EPM-90, 1-Channel)
SD-27-5031

Above left frame rail in front of the cab, under hood;
occasionally near accessory axles, such as lift axles

Smart relay valve to control service pressure on the steer axle or on
undriven axle(s). Note: Vehicles may have between one (1) and three
(3) 1C EPMs, depending on the axle configuration and layout.

Electro-Pneumatic Module
(EPM-90, 2-Channel)
SD-27-5031

Frame rail or crossmember close to
the controlled axle(s)

Smart relay valve to control service pressure on the drive axle(s) or
undriven axle(s). Note: Vehicles may have between one (1) and three
(3) 2C EPMs, depending on the axle configuration and layout.

GSBC Central ECU (EBS-90)
SD-27-5023V (This Document)

Under or immediately behind the cab
on the frame rail

Controls the entire GSBC system and provides an interface between
the vehicle and the GSBC system.

Electronic Trailer Pressure Control
Module (eTPCM-90)
SD-27-5036

Back of cab, close to the
trailer air lines

An electro-mechanical relay valve to send
control pressure to the trailer.

Modulator (M-50QR)
SD-27-5170

Frame rail near the left and right steer wheels

Provide steer wheel specific modulation of air pressure to avoid wheel
lockup and provide vehicle stability.

Wheel Speed Sensor (WS-24)
SD-13-4860

On the axle near the brake rotor or hub

Provide individual wheel speed information to the EPM.

Steering Angle Sensor (SAS-80)
SD-27-4709

Within the steering column under the steering wheel

Provide driver steering wheel input information for ESP purposes.

GSAT System
SD-24-250V

On the chassis connected to the air dryer, reservoirs,
and other pneumatic circuits

Cleans, controls, and distributes air to the brake reservoirs
and air-operated accessories on the vehicle.
Electronically controls parking brake and trailer supply air functions.

Table 1 – GSBC System Component Locations
SYSTEM COMPONENTS COMPARISON
For technicians familiar with previous generations of Bendix brake control systems, valves and components included
with GSBC may not look familiar. The following table is provided to help compare the new GSBC components and the
Bendix® EC-80® Electronic Control Unit (ECU) brake control system components:
EC-80 SYSTEM
COMPONENTS
Foot Brake Valve (FBV)
Pressure Sensors (PS-60)
Traction Relay Valve
(ATR-6/AT-3, R-12, or R-14)
HSA/Traction Solenoid
(AT-3, RV-3, DC-4)
Electronic Control Unit (EC-80)
Yaw Rate Sensor (YAS-70)

GSBC SYSTEM COMPONENTS

DIFFERENCES WITH GSBC

Foot Brake Module (FBM-40)

FBM now includes sensing technology to detect brake requests
from the driver. Includes dual-circuit brake control valve for
Pneumatic Backup Mode.

Electro-Pneumatic Module
(EPM-90, 1C or 2C variant)

The EPM is available in 1C and 2C variants. The EPM integrates the ATC valve,
relay valve functionality, and pressure sensors, and is capable of delivering air
pressure requested by the driver or driver assistance system.

GSBC ECU (EBS-90)

The GSBC ECU (Central ECU) is a frame-mounted ECU.
The YRS is now included in the Central ECU.

Modulator (M-40QR/M-40HF)

Modulator (M-50QR)

The modulator is now only used on the steer axle.

Steering Angle Sensor (SAS-80)

Steering Angle Sensor (SAS-80)

The SAS has not changed significantly for GSBC.

Wheel Speed Sensor (WS-24)

Wheel Speed Sensor (WS-24)

The WSS has not changed significantly for GSBC on Volvo vehicles.

Electronic Trailer
Pressure Control Module
(eTPCM-90)

The eTPCM is an electronically controlled relay valve and has replaced the trailer
pressure modulator. In conjunction with GSAT, it also provides tractor protection
system functionality.

GSAT (Global Scalable Air Treatment)
System

GSAT provides air treatment, governor, circuit isolation/protection, park control,
tractor protection, trailer supply/emergency functionalities.

Trailer Pressure Modulator
(M-40QR/M-40HF)
Tractor Protection Valve
(TP-3DC/TP-5)
Air Dryer (AD-IP, AD-IS, AD-HF)
Governor (D-2)
Intellipark
Dash Valve (MV-3/PP-DC)

Table 2 – Bendix EC-80 System and GSBC System Component Comparison

SD-27-5023V Rev 002 Bendix® GSBC® System and EBS-90™ (Global Scalable Brake Control System and Electronic Control Unit)

11

System Schematics

GSBC SYSTEM PNEUMATIC SCHEMATIC EXAMPLE (WITH GSAT)

15 16

13

20

8

15 16
6

17

15 16

9

9

7
10

14

21

11
12

12

18 19

3

14

5

1

4
5

2

8

9

15 16

15 16

9
15 16

COLOR CODING OF BRAKE SYSTEMS PER TMC RECOMMENDED PRACTICE #423
Charging

Primary

Secondary

Trailer (Supply)

Trailer (Control)

Parking (Control)

Accessories

Figure 11 – GSBC System Pneumatic Schematic Example* (With GSAT)
*This schematic is representative only and may differ from your vehicle. Verify your vehicle schematic with your OEM.
NOTE: In most applications of GSBC, the primary circuit is connected to the steer axle, and the secondary circuit is connected to the drive
axle(s) unlike most conventional U.S. plumbing configurations.
ITEM

COMPONENT

ITEM

COMPONENT

ITEM

COMPONENT

1

AIR COMPRESSOR

8

FOUNDATION BRAKE WITH SERVICE
CHAMBER

15

BENDIX® WS-24™ WSS

2

BENDIX® GSAT® AIR
TREATMENT MODULE

9

FOUNDATION BRAKE WITH SPRING
BRAKE CHAMBER

16

WSS CLAMPING SLEEVE

3

PRIMARY RESERVOIR

10

BENDIX® GSBC® FBM-40™ FOOT BRAKE
MODULE

17

BENDIX® SAS-80™ STEER ANGLE
SENSOR

4