Speed Sensor Input

9

LWS B Signal

Output voltage of LWS B Sensor

10

LWS A Signal

Output voltage of LWS A Sensor

11

LWS A Ground

Provides ground for Lining Wear Sensor

12

Unused

Unused

Table 4 – 1C and 2C EPM X2 Pin Description
6

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

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

X3

X3

X4
(unused)

X4
(unused)

Figure 10 – 2C EPM Electronic Connectors X3 and X4
CONNECTOR

PIN
Wheel Speed Sensor (WSS)

Lining Wear Sensor (LWS)

X3

(2C EPM Only)

N/A
Wheel Speed Sensor (WSS)

Lining Wear Sensor (LWS)
N/A

Figure 11 – X3 Electrical Pinout
SIGNAL

FUNCTION

1

WSS C High

Speed Sensor Input

2

WSS C Low

Speed Sensor Input

3

LWS D Ground

Provides ground for Lining Wear Sensor

4

LWS C Supply

Provides supply voltage for Lining Wear Sensor

5

LWS D Supply

Provides supply voltage for Lining Wear Sensor

6

Unused

Unused

7

WSS D High

Speed Sensor Input

8

WSS D Low

Speed Sensor Input

9

LWS D Signal

Output voltage of LWS B Sensor

10

LWS C Signal

Output voltage of LWS A Sensor

11

LWS C Ground

Provides ground for Lining Wear Sensor

12

Unused

Unused

Table 5 – 2C EPM X3 Pin Description

IMPORTANT
The X3 connector is not used on all vehicles. If not
plugged into the vehicle harness, the X3 connector
should be covered with a dust plug. Failure to do so
may lead to corrosion of the pins which may cause
issues and eventual EPM failure. Contact the OEM for
dust plug ordering information.
The X4 connector does not require a dust cover as it
is an unused connector without pins.

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

7

EPM-90 PNEUMATIC AND ELECTRICAL INTERFACES (CONT.)

Figure 12 – 1C EPM Electrical and Pneumatic
Schematic

Figure 13 – 2C EPM Electrical and Pneumatic Schematic

TRUCK CHASSIS MODIFICATIONS
If the vehicle’s chassis components are altered, (for example,
a wheel base extension or reduction; tag axle addition or
removal; a major body change such as conversion of a
tractor into a truck; or an axle, suspension, or steering
system component modification) the GSBC ECU must
be updated to reflect these changes. Contact your OE
vehicle manufacturer prior to making any modifications to
your vehicle.

If you modify your vehicle and do not update the
GSBC ECU, the GSBC system may fail to function as
intended. Serious vehicle braking and performance
issues could result, including unnecessary ESP system
interventions, exceeding regulated stopping distance,
and/or system faults leading to loss of electronic
functions. These types of failures can lead to a
loss-of-control of the vehicle, potential collisions,
property damage, serious injuries, and/or death.

8

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

GSBC SYSTEM PNEUMATIC SCHEMATIC EXAMPLE (WITH OPTIONAL GSAT)

15 16

13

20

15 16
6

17

8

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 14 – GSBC System Pneumatic Schematic Example* (With Optional 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

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 6 – GSBC System Schematic Example Components
SD-27-5031 Rev 001 Bendix® GSBC® EPM-90™ (Global Scalable Brake Control Electro-Pneumatic Modulator)

9

TROUBLESHOOTING
SOFTWARE TROUBLESHOOTING
The GSBC system will log DTCs when a fault is detected.
Depending on the severity of the DTC and which features
are impacted, one or more warning lamps may be displayed
to the driver on the dashboard. Refer to BW8207 GSBC
Operator’s Manual on B2Bendix.com for more information.
To appropriately diagnose, troubleshoot, and repair faults,
connect to the vehicle using Bendix® ACom® Diagnostic
Software or an appropriate OEM diagnostic software. For
more information regarding DTCs impacting EPMs, refer to
the Diagnostic Trouble Code (DTC) and Service Information
section on page 21.

TEST PREPARATION
Prior to conducting any troubleshooting testing, perform
the following steps:
1. Ensure that the vehicle is in a location where it can
be safely worked on.
2. Scan for any active faults in the GSBC System
using the appropriate diagnostic tool and save
the results.

For all troubleshooting tests and procedures, be sure
to disable the vehicle’s electrical supply and drain all
reservoirs of air pressure before removing fittings.
Failure to remove pressure from the pneumatic system
could lead to serious injury.
NOTE: Before performing any troubleshooting procedures,
check that the EPM is clean and clear of debris per the
Maintenance section of this document.

PNEUMATIC FUNCTION TEST
This test procedure confirms that the EPM is
receiving control pressure and supply pressure, and
is responding appropriately to driver braking requests.

IMPORTANT
Before performing this test, ensure that the braking
system is operating in electronic mode. This test can
not be completed successfully if the braking system
is not in electronic mode. Typically, a red “EBS” or
“BRAKE” warning lamp on the dashboard is indicative
of a braking system that is not operating in electronic
mode.

NOTE: During all tests, listen for audible leaks. If audible
leaks are observed, refer to the next section to troubleshoot
leakage.
To perform the pneumatic test for the EPM, complete the
following steps:
1. Chock the wheels on the vehicle to prevent
unintended movement.
2. Turn the vehicle on and build the air system
pressure to governor cut-out.
3. Release the parking brakes.
4. Confirm that the vehicle is in electronic mode. If the
system faults, read the troubleshooting code using
the appropriate diagnostic software. Troubleshoot
the faulted component using the applicable service
data sheet.
5. Turn the engine off in order to better hear the
operation of the EPM solenoids. NOTE: An
additional technician may be required to listen for
EPM solenoid activation.
6. With the engine off, and ignition power on, make
a series of light brake applications. The EPMs
will activate and the internal solenoids will make
audible ‘clicking’ noises as pressure is delivered.
7. Check for any system-generated faults using
Bendix ACom Diagnostic Software or the
appropriate OEM service tool.
8. Park the truck, turn off the ignition, and drain all
reservoirs on the truck.

Be sure to remove all supply air from the system prior
to installing any pressure gauge into the air system.
Failure to do so can result in injury.
9. Install a pressure gauge in port 1 (supply) of the
EPM and on one of the delivery ports of the same
EPM (for a 1C EPM, Port 2 or for a 2C EPM, Port
21 or 22).
10. Unplug the electrical connector from the FBM to
put the system into pneumatic backup mode. For
more information on the FBM and how to unplug
the electrical connector, refer to SD-27-5028 on
B2Bendix.com.
11. Release the parking brakes.
12. Restart the truck and build air system pressure to
governor cut-out.

Diagnose and repair any faults preventing the system
from entering Electronic Mode prior to continuing this
test.

10

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

TROUBLESHOOTING (CONT.)
PNEUMATIC FUNCTION TEST (CONT.)
13. Measure the pressure in the supply port using
the pressure gauge. If supply pressure is less
than indicated on the dashboard, ensure that the
measured supply pressure is being compared
to the correct reservoir/circuit. If the circuit is
correct and pressure is low, inspect the air line
between port 1 on the EPM and the reservoir for
kinks, blockages or damage. Repair the air line
as necessary to ensure that supply pressure is
reaching the EPM.

15. Release the service brake application using the
foot brake pedal. Measure the pressure in the
delivery port using the pressure gauge. Using the
gauge, check that the delivery pressure coming
out of the EPM has fallen to zero pressure on the
gauge.
If pressure does not respond as expected, complete
the following:
»

If pressure does not decrease at all or
falls slowly, remove the silencer from the
exhaust (port 3) to check for a blocked
exhaust. If this corrects the issue, replace
the silencer per instructions on page 18 of
this document.

»

If pressure does not increase as expected,
complete the following:

If pressure is still trapped, remove the
silencer from the FBM and perform
the same check. If this corrects the
issue, replace the FBM silencer per
the instructions in the FBM SD sheet,
SD-27-5028 on B2Bendix.com.

»

»

If pressure does not increase at all, double
check the plumbing and pressure gauges
for proper operation. Ensure that the
correct line is being measured.

If pressure is still trapped, inspect the air
lines between the FBM and the EPM,
looking for blockages, kinks, or other
obstructions.

»

»

Inspect the EPM delivery port(s) and the
attached fittings.

»

Confirm that the FBM is delivering control
pressure to the EPM. If pressure is being
supplied by the FBM and no pressure is
being delivered from the EPM, replace
the EPM.

If pressure is still trapped and no other
blockages are found in the air lines,
fittings, FBM, or exhaust port(s), replace
the EPM.

»

If pressure is not being supplied by
the FBM, refer to SD-27-5028 on
B2Bendix.com for FBM troubleshooting
instructions.

14. Make and hold a moderate service brake application
using the foot brake pedal. Measure the pressure in
the delivery port using the pressure gauge. Using
the gauge, check for delivery pressure coming out
of the EPM. Delivered pressure should be roughly
proportional to the movement of the foot brake pedal.

NOTE: Installing a gauge in the control port
(port 4) of the EPM can help to diagnose this
scenario. Pressure should not remain trapped
on the control port of the EPM without a service
brake application.
16. When diagnostic tests have been completed,
reconnect the FBM electrical connector and
remove any diagnostic pressure gauges from
the air system.
17. Reapply the parking brakes and go to the
Installation Test section on page 17 to validate
any repairs that have been performed.

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