SD-27-5170
Bendix® GSBC® M-50QR™ (Global Scalable Brake Control Quick
Release Antilock Modulator)
DESCRIPTION
The Bendix® GSBC® M-50QR™ (Global Scalable Brake
Control Quick Release Antilock Modulator), known
hereafter as “modulator” or “M-50QR,” is a high-capacity,
on/off air control device that incorporates a pair of electrical
solenoids used for control of the service brakes when
advanced braking system functions require individual
brake control of the steer axle. GSBC-equipped vehicles
have two modulators in total, which are used to precisely
modulate the air in the service actuators on the steer axle.
The M-50QR consists of a die cast, anodized, metal and
plastic body that houses two solenoids. One solenoid is
normally open and when energized, exhausts air at the
service actuator. The other solenoid is a normally closed
and when energized, holds back brake air from passing
through the modulator from the control system to the
service actuator.
There are two threaded metric straight thread o-ring
pneumatic ports. Both are M22 x 1.5 per the ISO-4039-2
standard.
The modulator is electrically controlled by the GSBC®
EBS-90™ (Electronic Control Unit), known hereafter as
“Central ECU,” through an electrical connector that is
ingress protection rated. Two through holes in the die cast
metal body are provided for mounting.
The supply and delivery ports on the modulators have
embossed identification codes. See Figure 2.

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.

Figure 1 – GSBC® M-50QR™ Modulator

TABLE OF CONTENTS
DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
M-50QR PNEUMATIC AND ELECTRICAL
INTERFACES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
GSBC SYSTEM SCHEMATIC EXAMPLE . . . . . . . . . . 4
OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Functional Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . 8
Software Troubleshooting . . . . . . . . . . . . . . . . . . . . 8
Test Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Pneumatic Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Leakage Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Electrical Component and Harness Test . . . . . . . . 10
REPLACEMENT INSTRUCTIONS . . . . . . . . . . . . . . . 11
Modulator Removal . . . . . . . . . . . . . . . . . . . . . . . . 11
Component Mounting . . . . . . . . . . . . . . . . . . . . . . 11
Modulator Installation . . . . . . . . . . . . . . . . . . . . . . 12
MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
DTC AND SERVICE INFORMATION . . . . . . . . . . . . . 14
Service Action Codes . . . . . . . . . . . . . . . . . . . . . . 16

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.

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.
2

SD-27-5170 Rev 000 Bendix® GSBC® M-50QR™ (Global Scalable Brake Control Quick Release Antilock Modulator)

M-50QR PNEUMATIC AND ELECTRICAL INTERFACES
Port 2

Port 1

Electrical
Connector

PORT

FUNCTION

PORT
THREADING

Port 1

Supply
(incoming air
from steer axle
1C EPM)

M22 x 1.5
ISO-4039-2

Port 2

Delivery
(air delivery
to service
actuators)

M22 x 1.5
ISO-4039-2

Port 3

Exhaust

N/A

Table 1 – M-50QR Pneumatic Port Information
NOTE: Refer to the fitting manufacturer’s torque
specifications before tightening the fittings.

Port 3 (Exhaust)
Figure 2 – M-50QR Modulator Features

1

PIN NO.

2
3

Figure 3 – M-50QR Modulator Electrical
Connection

3

2

DESCRIPTION

1

Exhaust/Outlet

2

Common/Source

3

Hold/Inlet

Table 2 – M-50QR Electrical
Pinout

Figure 4 – M-50QR Modulator Electrical Pinout
Electronic Component
Pneumatic Component

1
Electronic

Pin 1: Exhaust/Outlet
Pin 2: Common/Source
Pin 3: Hold/Inlet

1

3

Pneumatics

Port 1: Supply
Port 2: Delivery
Port 3: Exhaust

2
Figure 5 – M-50QR Electronic and Pneumatic Schematic

SD-27-5170 Rev 000 Bendix® GSBC® M-50QR™ (Global Scalable Brake Control Quick Release Antilock Modulator)

3

GSBC SYSTEM SCHEMATIC (WITH OPTIONAL GSAT) EXAMPLE
15 16

13

20

8

15 16
6

17

15 16

9

9

7
10
14
21

11
12

12

9

9

18 19

3

14

5

1

4
5

2

8

15 16

15 16

15 16

Figure 6 – GSBC System Schematic (with Optional GSAT) Example*
*This schematic is representative only and may differ from your vehicle. Verify your vehicle schematic with your OEM.
NOTE: In most applications, 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™ WHEEL SPEED
SENSOR

2

BENDIX® GSAT® AIR
TREATMENT MODULE

9

FOUNDATION BRAKE WITH SPRING
BRAKE CHAMBER

16

WHEEL SPEED SENSOR CLAMPING
SLEEVE

3

PRIMARY RESERVOIR

10

BENDIX® GSBC® FBM-40™ FOOT BRAKE
MODULE

17

BENDIX® SAS-80™ STEER ANGLE
SENSOR

4

SECONDARY RESERVOIR

11

BENDIX® GSBC® EPM-90™ ONE CHANNEL
ELECTRO-PNEUMATIC MODULE (EPM-1C)

18

BENDIX® GSBC® EBS-90™ CENTRAL
ECU

5

DRAIN VALVE

12

BENDIX® GSBC® EPM-90™ TWO CHANNEL
ELECTRO-PNEUMATIC MODULE (EPM-2C)

19

BENDIX® GSBC® EBS-90™ CENTRAL
ECU MUD COVER

6

TRAILER CONTROL
GLADHAND

13

BENDIX® GSBC® ETPCM-90™ ELECTRONIC
TRAILER PRESSURE CONTROL MODULE

20

ELECTRONIC PARKING BRAKE
HAND CONTROL UNIT (HCU)

7

TRAILER SUPPLY
GLADHAND

14

BENDIX® GSBC® M-50QR™ QUICK
RELEASE ANTILOCK MODULATOR

21

QUICK RELEASE VALVE (OPTIONAL)

®

Table 3 – GSBC System Schematic Example Components

4

SD-27-5170 Rev 000 Bendix® GSBC® M-50QR™ (Global Scalable Brake Control Quick Release Antilock Modulator)

APPLICATIONS
Modulators may be used for various purposes on a vehicle,
including the Anti-lock Braking System (ABS) and stability
interventions. For vehicles equipped with GSBC, the
modulator is located on the steer axle and is typically the
last component through which air passes on its way to the
service brake actuator. See Figure 6 for an example GSBC
system schematic.

OPERATION
GENERAL

Table 4 shows the various operational modes of the
modulator. The first four rows show normal vehicle braking
where the modulator does not intervene. In the case of a
rapid, non-antilock release of the brakes (e.g. if the driver
releases the brakes after a severe brake application),
the modulator helps to rapidly release air from the brake
chamber by providing a high-capacity exhaust path for
released air close to the brake chamber. The final four rows
show the actions taken during an antilock braking event.

NON-ANTILOCK BRAKE APPLICATION
During normal, non-antilock braking, both solenoids are deenergized and do not modify the operation of the modulator.
Brake application air enters the supply port of the modulator
and flows to the exhaust diaphragm. Air pressure, along
with spring force, seats the exhaust diaphragm on the
exhaust passage, thus preventing the escape of service
air. Simultaneously, application air flows to the supply
diaphragm and forces it away from its seat. Air flows past
the open supply diaphragm and out the modulator delivery
port to the service brake chambers.

NON-ANTILOCK HOLD
When the desired air pressure is attained in the service