SD-27-5031
Bendix® GSBC® EPM-90™ (Global Scalable Brake Control
Electro-Pneumatic Modulator)
INTRODUCTION
The Bendix® GSBC® EPM-90™ (Global Scalable Brake
Control Electro-Pneumatic Modulator), hereafter known
as “EPM,” is a pneumatic service brake control valve that
can be controlled either electronically or pneumatically.
The EPM is intended for installation on the chassis of
commercial vehicles, and is an important part of the
Bendix® GSBC® (Global Scalable Brake Control) system.
The EPM can control the service brakes on individual or
multiple axle(s), depending on vehicle configuration and
system features. The EPM is designed to function as part
of the larger GSBC system and will not function properly
in any stand-alone applications.
The EPM is available in a 1-Channel (1C) and a 2-Channel
(2C). The 1C and 2C EPMs can be easily distinguished
from each other by looking at the number of exhaust ports
on the EPM, which correlate directly to the number of
channels offered by a particular EPM. One exhaust port
means the component is a 1C EPM (see Figure 6), and
two exhaust ports means the component is a 2C EPM
(see Figure 7).

Figure 1 – GSBC 1C EPM (1-Channel)

The EPM is designed to receive both electronic and
pneumatic control signals from the GSBC system,
depending on the brake system’s mode of operation.
Both the 1C and 2C EPM operate at a nominal voltage of
24V. Both components are directly connected to the GSBC®
EBS-90™ (Central Electronic Control Unit) known hereafter
as “Central ECU,” which provides supply voltage to each
EPM on the vehicle.

Incorrect identification or plumbing of the primary or
secondary circuit(s) at the GSBC® EPM-90™ could lead
to serious vehicle braking, instability, and performance
issues, and/or collisions causing property damage,
serious injuries, and/or death. Contact your vehicle
manufacturer for up-to-date pneumatic brake system
schematics if work is being performed on the
braking system of the vehicle, or if the EPM requires
replacement.

Figure 2 – GSBC 2C EPM (2-Channel)

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.

A change in vehicle braking characteristics or a
dashboard warning lamp may indicate a malfunction
in the braking system. Although the vehicle air brake
system may continue to function, the vehicle should
not be operated until the necessary repairs have been
made by a qualified technician.
Always check the vehicle braking system for proper
operation after performing service or maintenance and
before returning the vehicle to service.

2

After removal and replacement of the EPM, special
considerations need to be taken to ensure the EPM has
been properly installed on the vehicle. These include:
• Location and orientation of the EPM
• Correct plumbing of the EPM
• Installation test to verify proper installation, refer
to the Replacement Instructions section.

SD-27-5031 Rev 001 Bendix® GSBC® EPM-90™ (Global Scalable Brake Control Electro-Pneumatic Modulator)

OPERATION

PNEUMATIC BACKUP MODE OPERATION

OPERATION OVERVIEW
The 1C and 2C EPMs are installed rigidly on the exterior
of the vehicle, usually on the chassis or the frame. They
are typically located close to the axle or axle(s) that they
control, and can be located on a vehicle by following an
air line up from the brake chamber.
The 1C and 2C EPMs primarily act as an electronicallycontrolled relay valve. Based on driver or system demand,
they are capable of applying service brake pressure of any
value between zero and system pressure to the wheel ends
they are connected to.

While in pneumatic backup mode, the pneumatic pressure
delivered by the Bendix® GSBC® FBM-40™ (Global Scalable
Brake Control Foot Brake Module), hereafter known as
“FBM,” will control the pressure to the brake chambers
via the relay valve in the EPM. The EPM will function as a
relay valve and deliver the pressure present at the control
port through entirely mechanical means. For an example
of pneumatic backup mode operation, see Figure 4.
For a full system schematic example, refer to Figure 14
on page 9.

ELECTRONIC MODE OPERATION
When the EPM is electrically powered and operating
without errors, it will receive requests from the Central
ECU, communicated over the digital connection between
the Central ECU and the EPM. For an example of primary
electronic mode operation, see Figure 3.
When operating in primary (electronic) mode, the 1C EPM
can deliver a single pressure to connected wheel ends
delivered by port 2, and is typically used to control the steer
axle of a vehicle. It is also used to control liftable axles. For
1C EPM port identification, see Figures 5 and 6.
When operating in primary (electronic) mode, the 2C EPM
can deliver two separate and independent pressures to
connected wheel ends – one pressure delivered by port
21, and the other by port 22. 2C EPMs are typically used
to control the drive axle(s) of a vehicle. For 2C EPM port
identification, see Figure 7.

Driver Brake
Demand

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.

Deceleration Demand

GSBC® EBS-90™
Central ECU

Pneumatic Signal
Digital Control Signal

Electronic
Pressure
Demand

Electronic CAN Signal
Wheel Speed Signal
Wheel Speed Signal

GSBC®
FBM-40™

Wheel Speed
Sensor

Brake Control Pressure
Service Brake Pressure

Supply Pressure

GSBC® EPM-90™

Foundation
Brakes

Reservoir

Figure 3 – GSBC Electronic Mode Example
Pneumatic Signal
GSBC® EBS-90™
Central ECU

GSBC®
FBM-40™

Wheel Speed
Sensor

Brake Control Pressure
Service Brake Pressure

Supply Pressure

GSBC® EPM-90™
Reservoir

Foundation
Brakes

Figure 4 – GSBC Pneumatic Backup Mode Operation Example
SD-27-5031 Rev 001 Bendix® GSBC® EPM-90™ (Global Scalable Brake Control Electro-Pneumatic Modulator)

3

EPM-90 PNEUMATIC AND ELECTRICAL INTERFACES
PNEUMATIC PORTS

Electrical
Covering
Cap

Port 4
Port 2
Port 2

Port 1

“Port” 3
(Exhaust)
Figure 5 – 1C EPM Pneumatic Ports (Front)
PORT

FUNCTION

PORT
THREADING

MAXIMUM
FITTING
TORQUE

1

Valve supply
pressure

M22 x 1.5

Max 80 N•m
(59 ft-lbs)

2
(1C EPM,
common
delivery)

Valve delivery
pressure

M22 x 1.5

Max 80 N•m
(59 ft-lbs)

3

Valve exhaust (to
atmosphere)

N/A

Refer to Silencer in
Replacement Parts

4

Control pressure
(for pneumatic
backup operation)

M16 x 1.5

Max 55 N•m
(40.6 ft-lbs)

Figure 6 – 1C EPM Pneumatic Ports (Back)

IMPORTANT
All pneumatic fitting ports on both the 1C and 2C
EPM are metric. ONLY USE metric straight thread
O-ring fittings on this component. Failure to use the
correct fittings may result in air leakage and permanent
damage to the component.

Table 1 – 1C EPM Pneumatic Port Information

4

SD-27-5031 Rev 001 Bendix® GSBC® EPM-90™ (Global Scalable Brake Control Electro-Pneumatic Modulator)

EPM-90 PNEUMATIC AND ELECTRICAL INTERFACES (CONT.)
PNEUMATIC PORTS

Electronic
Connector
Cover

Electrical
Covering
Cap
Port 4

Port 22

Port 21
Port 1
“Port” 3 (Exhaust)
Figure 7 – 2C EPM Pneumatic Ports
PORT

FUNCTION

PORT
THREADING

MAXIMUM
FITTING
TORQUE

1

Valve supply
pressure

M22 x 1.5

Max 80 N•m
(59 ft-lbs)

21, 22
(2C EPM,
two separate
delivery
channels)

Valve delivery
pressure

M22 x 1.5

Max 80 N•m
(59 ft-lbs)

3

Valve exhaust
(to atmosphere)

N/A

Refer to Silencer in
Replacement Parts

4

Control pressure
(for pneumatic
backup
operation)

M16 x 1.5

Max 55 N•m
(40.6 ft-lbs)

IMPORTANT
All pneumatic fitting ports on both the 1C and 2C
EPM are metric. ONLY USE metric straight thread
O-ring fittings on this component. Failure to use the
correct fittings may result in air leakage and permanent
damage to the component.

Table 2 – 2C EPM Pneumatic Port Information

SD-27-5031 Rev 001 Bendix® GSBC® EPM-90™ (Global Scalable Brake Control Electro-Pneumatic Modulator)

5

EPM-90 PNEUMATIC AND ELECTRICAL INTERFACES (CONT.)
ELECTRICAL CONNECTORS

For pin descriptions, refer to:

The 1C EPM has two (2) electrical connectors, X1 and X2.
The 2C EPM has three (3) electrical connectors, X1, X2,
and X3, with X4 as an unused connector.
Regardless of EPM variant, the electrical connectors are
protected from dirt and debris by a removable Electronic
Covering Cap. The 1C EPM has one cover, and the 2C
EPM has two. Refer to the Replacement Parts section of
this document for the appropriate part number.

•

Table 3: X1 Pin Description

•

Table 4: X2 Pin Description

•

Table 5: X3 Pin Description

X2

X2

X1

Figure 8 – 1C and 2C EPM Electronic Connectors X1
and X2
CONNECTOR

X1

(1C & 2C EPM)

X1

PIN

SIGNAL

Figure 9 – X1 and X2 Electrical Pinout

FUNCTION

1

Ground

Supply ground from Central ECU

2

Supply

Supply voltage from Central ECU

3

CAN High

CAN Network Interface

4

CAN Low

CAN Network Interface

Table 3 – 1C and 2C EPM X1 Pin Description
CONNECTOR

PIN
Wheel Speed Sensor (WSS)

Lining Wear Sensor (LWS)

X2

(1C & 2C EPM)

N/A
Wheel Speed Sensor (WSS)

Lining Wear Sensor (LWS)
N/A

SIGNAL

FUNCTION

1

WSS A High

Speed Sensor Input

2

WSS A Low

Speed Sensor Input

3

LWS B Ground

Provides ground for Lining Wear Sensor

4

LWS A Supply

Provides supply voltage for Lining Wear Sensor

5

LWS B Supply

Provides supply voltage for Lining Wear Sensor

6

Unused

Unused

7

WSS B High

Speed Sensor Input

8

WSS B Low