24

EPM3, PCL1, Backup
Solenoid Valve: Circuit
Current Below Threshold

EPM internal electrical failure.

G

0x50E22B

20706

43

EPM3, PCL1, Backup
Solenoid Valve: Signal Cross
Coupled

EPM internal electrical failure.

G

0x50E367

20707

103

EPM, Pneumatic Backup
Circuit: Signal Incorrect After
Event

Temporary Brake Test Failure: EPM reports
insufficient pressure delivered by FBM.

BB

0xD0011F

49153

31

Lost Communication With
EPM0: Circuit Intermittent

EPM internal electrical failure.

G

0xD0018F

53249

143

Lost Communication With
EPM0: Erratic

Inconsistent communications between EPM
and GSBC ECU.

CC

0xD0021F

53250

31

Lost Communication With
EPM1: Circuit Intermittent

EPM internal electrical failure.

G

0xD0028F

53250

143

Lost Communication With
EPM1: Erratic

Inconsistent communications between EPM
and GSBC ECU.

CC

0xD0031F

53251

31

Lost Communication With
EPM2: Circuit Intermittent

EPM internal electrical failure.

G

0xD0038F

53251

143

Lost Communication With
EPM2: Erratic

Inconsistent communications between EPM
and GSBC ECU.

CC

0xD0041F

53252

31

Lost Communication With
EPM3: Circuit Intermittent

EPM internal electrical failure.

G

0xD0048F

53252

143

Lost Communication With
EPM3: Erratic

Inconsistent communications between EPM
and GSBC ECU.

CC

Table 8 - Diagnostic Trouble Codes (DTCs)

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

35

DIAGNOSTIC TROUBLE CODE (DTC) AND SERVICE INFORMATION (CONT.)
SERVICE ACTION CODES
NOTE: Prior to servicing a vehicle, refer to the General Safety Guidelines on page 2.
SERVICE
ACTION CODE

RECOMMENDED SERVICE

A

Turn off vehicle power.
Check the cables and connectors between EPM and wheel-speed sensor for short circuit to battery power. If
wiring harness is found to have a short, repair or replace wiring harness per OEM guidelines.
Disconnect wheelspeed sensor electrical connector from EPM. Measure resistance between harness-side
sensor pins and vehicle power. Resistance must be greater than 200 kohms.
If resistance measurement is outside specified range, disconnect wheelspeed sensor from vehicle harness (if
applicable) and re-check sensor pins. If test fails, replace sensor. Otherwise, investigate vehicle harness per
OEM procedure for short circuit to battery voltage.
If no fault is found in WSS or in vehicle harness, replace the EPM.

B

Turn off vehicle power.
Check the cables and connectors between EPM and wheel-speed sensor for short circuit to vehicle ground. If
wiring harness is found to have a short, repair or replace wiring harness per OEM guidelines.
Disconnect wheelspeed sensor electrical connector from EPM. Measure resistance between harness-side
sensor pins and vehicle ground. Resistance must be greater than 200 kohms.
If resistance measurement is outside specified range, disconnect wheelspeed sensor from vehicle harness (if
applicable) and re-check sensor pins. If test fails, replace sensor. Otherwise, investigate vehicle harness per
OEM procedure for short circuit to battery voltage.
If no fault is found in WSS or vehicle harness, replace the EPM.

C

Check wheel speed sensor for damage. Replace sensor if it is mechanically damaged.
Check the cables and connectors between EPM and wheel-speed sensor for shorted or open circuits.
Remove wheel speed sensor connector from EPM. At wheel speed sensor wiring harness connector, measure
resistance across two pins of wheelspeed sensor harness. Resistance must be between 800 and 2000 ohms.
Measure resistance of between sensor pins and vehicle GND. Resistance must be greater than 200 kohms.
If either resistance measurement is outside measured range, disconnect wheelspeed sensor from vehicle
harness (if applicable) and re-check sensor pins. If test fails, replace sensor. Otherwise, investigate vehicle
harness per OEM procedure for short or open circuit.
Measure voltage between EPM GND and either wheel speed sensor pin (with the wheelspeed sensor
connected to the EPM electrical connector). Voltage must in range 0.5-4.3V. If voltage is not present and
harness is known good, proceed to next step.
Switch left and right WSS and repeat all tests above. If problem remains on the same side of the vehicle,
replace EPM. Otherwise, switch sensors back and replace indicated WSS/harness.

D

Check for sources of electronic noise on vehicle, including aftermarket electronic components. Disable
aftermarket components to see if fault returns.
If fault returns, then check wheel speed sensor for damage. Replace sensor if it is mechanically damaged.
Check the cables and connectors between EPM and wheel speed sensor for shorted or open circuits or
mechanical damage to sensor wiring harness. If faults are found, repair harness according to OEM instructions.
If no faults are found in the harness, replace the WSS.
If fault returns, measure WSS pins for high-frequency noise using an oscilloscope. If found, find and eliminate
source(s) of high-frequency noise.
If fault still returns, replace the EPM.

E

Mismatch between EPM and GSBC ECU EEPROM Dataset. Contact OEM for assistance in updating software
on GSBC ECU or EPMs.

F

Check pneumatic plumbing between EPM and supply pressure. Inspect EPM supply port (port 1) for blockage
or restriction, and repair as necessary.
On steer axles only, check pneumatic plumbing (air lines and fittings) between EPM and modulators. Inspect
EPM delivery ports (both ports labeled 2) for blockage or restriction, and repair as necessary. Inspect
modulator supply ports (port 1) for blockages or restrictions, and repair as necessary.
Check modulator operation using diagnostic tool. If any operational problems are found, repair or replace as
necessary.
Check that dash gauges are appropriately reporting system pressures. If dash gauges are incorrect or missing
information, diagnose and troubleshoot according to manufacturer instructions.
If no fault is found in plumbing, modulators, system pressure signal or other checked items, replace the EPM.

G

Clear fault. If fault returns, replace the EPM.

H

Inspect EPM for correct plumbing at pneumatic ports - refer to OEM plumbing schematics for proper
configuration. Inspect silencer by removing one or both (if equipped) from the EPM.
Power cycle the vehicle. If the fault returns, replace the EPM. If fault does not return, replace the silencer.

Table 9 - Service Action Codes for Recommended Service

36

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

DIAGNOSTIC TROUBLE CODE (DTC) AND SERVICE INFORMATION (CONT.)
SERVICE ACTION CODES (CONT.)
NOTE: Prior to servicing a vehicle, refer to the General Safety Guidelines on page 2.
SERVICE
ACTION CODE

RECOMMENDED SERVICE

J

Check if other EPMs have the same fault. If so, check the cables and connectors from the GSBC ECU to both
EPMs. Inspect wiring for chafing or shorts between both EPMs. Repair wiring or connector(s) found to be
damaged according to OEM procedure.
If other EPMs do not have the same fault, check for shorts between battery voltage and the indicated EPM.
Inspect wiring and connectors for damage or wear, and replace anything found to be damaged according to the
OEM procedure
Once corrected, fault will clear with a power cycle of the GSBC system.

K

Check the cables and connectors from the GSBC ECU to the EPM. Inspect wiring for chafing or shorts to either
ground or battery power. Repair any problem in the harness or electrical connector(s) found according to the
OEM procedure.
Check to see if a CAN Communication DTC is also active. If one is active, continue to troubleshoot wiring
harness until harness faults are found and corrected. Otherwise, if no CAN Communication DTC(s) are active,
and this DTC is still active, replace the EPM.
If replacing the EPM does not correct the error, replace the GSBC ECU.

L

Check the wiring harness and connectors from the GSBC ECU to the EPM. Inspect wiring for chafing or shorts
to either ground or battery power. Repair any problem in the harness or electrical connector(s) found according
to the OEM procedure.
Check that supply voltage at EPM is within 3V of GSBC ECU EPM Supply voltage. If the difference is more
than 3V, inspect harness for shorts to ground or failed wiring. Replace components necessary to correct the
condition according to OEM procedures.
Clear fault. If fault returns, replace the EPM.

M

Check the wiring harness and connectors from the GSBC ECU to the EPM. Inspect wiring for chafing or shorts
to either ground or battery power. Repair any problem in the harness or electrical connector(s) found according
to the OEM procedure.
Power cycle the vehicle.
If there is no CAN Communication DTC active, and this DTC remains active, replace the EPM. Otherwise,
continue to troubleshoot the wiring harness and electrical connectors until the source of the electrical fault is
determined.

N

Check wiring between EPM and GSBC ECU. Check for shorts to battery voltage between EPM supply pin
and sources of battery voltage. Inspect electrical connector at both ends (EPM and GSBC ECU) for damage,
shorts, or missing insulation.
Repair or replace wiring and/or electrical connectors as necessary per OEM instructions. Power cycle the
vehicle. If the fault is still active, continue as follows:
Turn vehicle off.
At GSBC ECU, disconnect electrical connector with this EPM on it (refer to manufacturer wiring schematic). At
disconnected electrical connector, on wiring harness side, measure resistance between EPM supply pin and
EPM ground pin. Then, measure resistance between EPM supply pin and vehicle ground. Both measurements
should be above 500 ohms.
If this is not the case, disconnect electrical harness connector from EPM, and repeat previous measurement.
If measurement is OK, then replace the EPM. Otherwise, repair wiring harness to eliminate the short.
If isolation resistance with electrical harness connected to the EPM is above the limit of 500 ohms, reconnect
everything and turn the truck back on. Check to see if the fault is still present. If the DTC is still active, replace
the GSBC ECU.

Table 9 - Service Action Codes for Recommended Service

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

37

DIAGNOSTIC TROUBLE CODE (DTC) AND SERVICE INFORMATION (CONT.)
SERVICE ACTION CODES (CONT.)
NOTE: Prior to servicing a vehicle, refer to the General Safety Guidelines on page 2.
SERVICE
ACTION CODE

RECOMMENDED SERVICE

P

Check the wiring between the EPM and the GSBC ECU. Check for shorts to battery voltage between EPM
supply pin and sources of battery voltage. Inspect the electrical connector at both ends (EPM and GSBC ECU)
for damage, shorts, or missing insulation.
Repair or replace wiring and/or electrical connectors as necessary per OEM instructions. Power cycle the
vehicle. If the fault is still active, continue as follows:
Ensure that truck is parked and chocked. Electrical power truck. Unplug FBM electrical harness to put vehicle
into backup mode.
First, at the GSBC ECU, unplug the electrical connector that includes this EPM. Measure voltage at EPM
supply pin on ECU. If voltage is more than 4V, replace the GSBC ECU.
Next, if there is no voltage on the GSBC ECU EPM supply pin, measure for voltage on the corresponding EPM
supply pin on the vehicle harness. If voltage is more than 4V on the vehicle harness pin, short is within the
harness and coming from a component not located on the same GSBC ECU electrical connector.
Finally, if there is no voltage on the vehicle harness EPM supply pin, re-connect the electrical connector to the
GSBC ECU. At the EPM, remove the electrical connector and measure the voltage on the EPM supply pin. If
voltage is more than 4V, the short is within the harness and stems from something else on the same GSBC
ECU connector.
Once the source of the short is located, repair or replace wiring and/or electrical connectors as necessary per
OEM instructions. Power cycle the vehicle.

Q

Check wiring between the EPM and the GSBC ECU. Check for shorts between the EPM supply pin and
other electrical wires. Inspect electrical connector at both ends (EPM and GSBC ECU) for damage, shorts, or
missing insulation.
Repair or replace wiring and/or the electrical connectors as necessary per OEM instructions. Power cycle the
vehicle. If the fault is still active, continue as follows:
Turn vehicle off.
At the GSBC ECU, disconnect the electrical connector with this EPM on it (refer to manufacturer wiring
schematic). At disconnected electrical connector, on wiring harness side, measure resistance between the
EPM supply pin and the EPM ground pin. Then, measure the resistance between the EPM supply pin and the
vehicle ground. Both measurements should be above 500 Ohms.
If this is not the case, disconnect the electrical harness connector from the EPM, and repeat the previous
measurement.
If measurement is OK, then replace the EPM. Otherwise, repair wiring harness to eliminate the short.
If isolation resistance with electrical harness connected to the EPM is above the limit of 500 ohms, reconnect
everything and turn the truck back on. Check to see if the fault is still present. If the DTC is still active, replace
the GSBC ECU.

R

Check the wiring between the EPM and the GSBC ECU for damage, shorts, missing insulation or corrosion
damage.
Inspect the electrical connector at both ends (EPM and GSBC ECU) for damage, shorts, missing insulation or
corrosion damage.
Repair or replace wiring and/or electrical connectors as necessary per OEM instructions. Power cycle the
vehicle. If the fault is still active, continue as follows:
Turn vehicle off.
At GSBC ECU, disconnect the electrical connector with this EPM on it (refer to manufacturer wiring schematic).
At EPM, disconnect the electrical connector. Measure resistance between each end of the harness for each of
the 4 wires running to the EPM. Resistance of wires disconnected from both GSBC ECU and EPM should be
below 3 ohms.
If any wire exceeds a resistance of 3 ohms, repair or replace the wiring and/or connector as necessary per
OEM instructions. Reassemble the vehicle and confirm that the fault clears. If fault does not clear, investigate
components (EPM and GSBC ECU) for corrosion on electrical pins. If corrosion on electrical pins of
components is discovered, replace the component and correct the condition that allowed corrosion to form in
the first place.

S

Check the pinning of the power supply for the EPM at the GSBC ECU electrical connector, ensuring that the
electrical connector is pinned properly, and the EPM is receiving power. Check the wiring harness at both the
GSBC ECU and the EPM for incorrect pinning and correct if necessary. Contact the OEM to check/re-load the
configuration of the GSBC ECU.
If after updating the GSBC ECU configuration, if the DTC is only reported for some of the EPMs, replace those
EPMs individually. If the DTC is reported for all EPMs, replace the GSBC ECU.

Table 9 - Service Action Codes for Recommended Service

38

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

DIAGNOSTIC TROUBLE CODE (DTC) AND SERVICE INFORMATION (CONT.)
SERVICE ACTION CODES (CONT.)
NOTE: Prior to servicing a vehicle, refer to the General Safety Guidelines on page 2.
SERVICE
ACTION CODE

RECOMMENDED SERVICE

T

Let the GSBC system shut down properly. Switch on the system again. If failure is no longer active, no further
action is needed. If DTCs 0x504912..0x505212 (Lining Wear Supply Circuit) are active, check the lining wear
sensor wiring/connection and repair as necessary. If failure is still active after correcting Lining Wear Sensing
faults, replace the EPM.

U

The EPM is over temperature (248 degrees F/120 degrees C). Power off the vehicle, and wait for the vehicle
to cool off (roughly 1 hour). Inspect the location of the EPM to ensure that heat shields (if applicable) have not
been removed or rendered ineffective.
If the DTC is still present after temperatures have returned to normal, then replace the EPM.

V

The EPM is under temperature (-40 degrees F/C). Safely warm up the vehicle. Once the vehicle is warm, if the
failure is still present, then replace the EPM.

W

Check that the brake chamber air lines are connected to the correct ports in all GSBC devices.
Note that connecting the parking brake line to the EPM can cause this fault.
Check for leaks between the parking and service sides of all parking brake chambers. Carefully check the
EPM, FBM, and all air lines between the two for debris, damage, kinks, or blockages. Check the silencers on
both the EPM and the FBM for dirt, debris, or blockages. Repair or replace any faulty plumbing or silencers as
needed. Continue with troubleshooting below if issue persists.
Ensure that the reservoirs are fully charged (until cut-out pressure). Install a calibrated external pressure gauge
in the service brake chamber to use as a reference.
Apply 116 psi (~8 bar) of service brake pressure using the service brake pedal. Hold this application steady.
Next, in one movement, reduce measured service brake pressure to approximately 16 psi (~1.1 bar) on the
external gauge.
After one second, if pressure on the gauge is greater than 22 psi (~1.5 bar), check the EPM silencer for
blockage or debris. If the EPM silencer is OK, then the EPM should be replaced.
Next, unplug the FBM electrical connector to force the system into pneumatic backup mode. Ensure that the
reservoirs are fully charged (until cut-out pressure). Apply 30 psi (~2 bar) of service brake pressure using the
service brake pedal. Hold this application steady. Next, in one movement, quickly and fully release the service
brake pedal.
After one second, if pressure on the gauge is greater than 5 psi, (~0.35 bar) then re-check the FBM silencer
and the air lines between the FBM and the EPM. If the FBM silencer is OK and the air lines are undamaged,
not blocked and in good condition, the the FBM should be replaced.
Reconnect the FBM and clear faults. If the issue persists, replace the GSBC ECU.

X

Check that the brake chamber air lines are connected to the correct ports in all GSBC devices.
Check for leaks between the parking and service sides of all parking brake chambers. Carefully check the
EPM, FBM, and all air lines between the two for debris, damage, kinks, or blockages. Check the silencers on
both the EPM and the FBM for dirt, debris, or blockages. Repair or replace any faulty plumbing or silencers as
needed. Continue with troubleshooting below if issue persists.
Ensure that the reservoirs are fully charged (until cut-out pressure). Install a calibrated external pressure gauge
in the service brake chamber to use as a reference.
Apply 116 psi (~8 bar) of service brake pressure using the service brake pedal. Hold this application steady.
Next, in one movement, reduce measured service brake pressure to approximately 16 psi (~1.1 bar) on the
external gauge.
After one second, if pressure on the gauge is greater than 22 psi (~1.5 bar), check the EPM silencer for
blockage or debris. If the EPM silencer is OK, then the EPM should be replaced.
Next, unplug the FBM electrical connector to force the system into pneumatic backup mode. Ensure that the
reservoirs are fully charged (until cut-out pressure). Apply 30 psi (~2 bar) of service brake pressure using the
service brake pedal. Hold this application steady. Next, in one movement, quickly and fully release the service
brake pedal.
After one second, if pressure on the gauge is greater than 5 psi, (~0.35 bar) then re-check the FBM silencer
and the air lines between the FBM and the EPM. If the FBM silencer is OK and the air lines are undamaged,
not blocked and in good condition, the the FBM should be replaced.
Reconnect the FBM and clear faults. If the issue persists, replace the GSBC ECU.

Y

Check that the brake chamber air lines are connected to the correct ports in all GSBC devices. Carefully check
the EPM, FBM, and all air lines between the two for debris, damage, kinks, or blockages. Check the silencers
on both the EPM and the FBM for dirt, debris, or blockages. Repair or replace any faulty plumbing or silencers
as needed.
Clear faults and test drive the vehicle. If the fault returns, replace the EPM. Clear faults and test drive the
vehicle. If fault returns, replace the FBM. Clear faults and test drive the vehicle. If fault returns, replace the
GSBC ECU.

Table 9 - Service Action Codes for Recommended Service
SD-27-5031 Rev 001 Bendix® GSBC® EPM-90™ (Global Scalable Brake Control Electro-Pneumatic Modulator)

39

DIAGNOSTIC TROUBLE CODE (DTC) AND SERVICE INFORMATION (CONT.)
SERVICE ACTION CODES (CONT.)
NOTE: Prior to servicing a vehicle, refer to the General Safety Guidelines on page 2.
SERVICE
ACTION CODE

Z

RECOMMENDED SERVICE

Carefully check the EPM, FBM, and all air lines between the two for debris, damage, kinks, or blockages.
Check the silencers on both the EPM and the FBM for dirt, debris, or blockages. Repair or replace any faulty
plumbing or silencers as needed.
Clear faults.
Install a pressure gauge at the control port of the EPM.
Make and release a service brake application using the service brake pedal.
If pressure is greater than 4.5 psi after releasing the pedal, inspect the air lines between the EPM and the
FBM for blockages or kinks. Inspect the FBM silencer, and clean/replace either the silencer or the FBM as
necessary.
If pressure is less than 4.5 psi after releasing the pedal, move the gauge to each delivery of the EPM (if
applicable). Make and release a service brake application using the service brake pedal. If pressure remains
after the pedal is released, inspect the EPM silencer(s) and either clean or replace the silencer as necessary.
Repeat the test. If pressure remains trapped, replace the EPM. If pressure does not remain trapped, test the
other channel/delivery of the EPM (if applicable).

AA

Check for and correct any faults in the air supply system prior to troubleshooting this fault. If there are no faults
in the air supply system, turn off the truck and drain both reservoirs to ambient pressure. Install an external
pressure gauge in the supply port of the EPM that is faulted. Start the truck and charge both reservoirs to cutout pressure.
Turn the truck off and wait at least 90 seconds without pressing the brake pedal. Then, turn the ignition back to
the “ON” position.
Compare the pressure reported by the dashboard air gauge in the reservoir feeding the EPM to the external
pressure gauge that was previously installed.
If the pressure on the external gauge is not within +/-10% of the pressure reported on the dashboard, inspect
air lines between the reservoir and the EPM for blockages, kinks, or other obstruction. Verify that both
reservoirs are charged by the air treatment system.
If the pressure measured on the external gauge is equal to that reported on the dashboard, replace the EPM.

BB

For each EPM channel, complete the troubleshooting steps below:
Install an external pneumatic pressure gauge at the control port of the EPM. Using the external gauge,
apply and release the service brakes. Confirm that pressure in the control port of the EPM rises and falls
appropriately with the brake pedal application.
If pressure does not rise or fall as expected, inspect the air line between the EPM and the FBM for kinks,
blockage, or obstruction. Repair or replace air lines as necessary.
If pressure rises but does not fall, remove the FBM silencer and the EPM silencer(s) and repeat the test. If this
corrects the issue, clean or replace the suspect silencer(s) as necessary.
If the air lines or silencers are not found to be damaged, install a pressure gauge in the delivery of the FBM
and repeat the test. If indicated pressure does not rise or fall as expected, replace the FBM. If the pressure
response is normal, inspect the air lines again to find the blockage preventing air from flowing.
If all other possible problems have been eliminated, replace the EPM.

CC

If all EPMs report this fault, update the GSBC ECU software. Contact the OEM for assistance in updating the
GSBC ECU.
If only one EPM is reporting the fault, check all wiring between the GSBC ECU and the EPM (including
checking for chafing damage, shorts, and opens). Check the electrical connector at the GSBC ECU and at the
EPM. Check if DTC clears by disconnecting the EPM from the electrical connector.
If all EPMs report the fault after checking the wiring and updating the GSBC ECU software, replace the GSBC
ECU.
If only one EPM continues to report this fault after checking the wiring, update the SW of that EPM. If the fault
does not clear, replace that EPM.

Table 9 - Service Action Codes for Recommended Service

40

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

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