SD-08-12000

Electronic Air Control (EAC) System - Integrated with Bendix® EC-80™
Electronic Control Unit (ECU)
INTRODUCTION
The Electronic Air Control (EAC) system is a set of software
functions that are integrated into a special version of the
Bendix® EC-80™ Electronic Control Unit (ECU).
The EAC system adds new and improved features
supporting the Bendix® AD-HFi™ air dryer including J1939
messaging, Diagnostic Trouble Codes (DTCs), advanced
functionality, and governor control.

DESCRIPTION
ELECTRONIC AIR CONTROL (EAC) SYSTEM
The Bendix EAC system adds intelligent electronic air
control of the air compressor governor. The EAC system
provides the basic governor operation to maintain safe air
pressure levels and provides advanced features, along with
air system diagnostic and prognostic information.
The EAC system communicates on the vehicle J1939 CAN
bus and receives vehicle information including primary
and secondary air pressures, engine speed, torque, and
other vehicle operational conditions. The EAC system also
transmits compressor state, diagnostic, and prognostic
information, including cartridge lifetime prediction, on the
vehicle CAN bus.

J1939 CAN HI

J1939 CAN LO

EAC
Bendix®
EC-80™

Beyond basic governor control, the EAC system has
advanced features to optimize air system pressure control
and conserve energy. Also, the EAC system has advanced
purge operations to protect the air system against moisture.

IMPORTANT
Bendix ® -brand Electronic Control Units (ECUs)
are not designed to store data for purposes of
accident reconstruction, and Bendix® ACom® PRO™
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.

X3, Pin 8 High

Compressor
Control
Solenoid

GND

Figure 1 – EAC System Diagram
1

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.

SYSTEM COMPONENTS
The Electronic Air Control (EAC) system is a set of
software functions that are integrated into a special version
of the Bendix® EC-80™ Electronic Control Unit (ECU).
•

2

Electronic Control Unit (ECU): The ECU controlling
the EAC system will be referred to as the EAC (EC80 integrated) ECU. The EAC system is controlled by
the integrated functionality located within the EC-80
ECU which receives air system pressure information
from the vehicle J1939 CAN bus and controls the air
compressor governor to maintain safe air pressure
levels. The EAC (EC-80 integrated) ECU monitors
the air system pressure. The unit energizes and
de-energizes the compressor solenoid governor to

unload and load the vehicle air compressor. The EAC
(EC-80 integrated) ECU also receives engine speed,
torque, and vehicle speed from the engine Electronic
Control Module (ECM) to provide advanced features.
The brake EAC system advises the driver of any
malfunctions. Diagnostic Trouble Codes (DTC) can
be displayed via Bendix® ACom® PRO™ Diagnostic
Software to evaluate system status.
•

Compressor Solenoid Governor: The compressor
solenoid governor is controlled by the ECU to load and
unload the air compressor.

•

Air Dryer (Bendix ® AD-HFi ™ SP Air Dryer and
Bendix® AD-HFi™ EP Air Dryer): The Electronic Air
Control (EAC) system supports either the AD-HFi
SP air dryer (200 cubic inch, standard purge tank)
or AD-HFi EP air dryer (300 cubic inch extended
purge tank). The vehicle EAC system has been
parameterized at the factory and therefore designed
for use with either an SP- or EP-size purge reservoir.
If the air dryer is replaced, use the OE service part to
ensure proper operation.

•

Air Compressor: The EAC system is configured with
the original equipment compressor only and therefore,
any replacement compressor must be the same make
and model.

•

EAC (Bendix® EC-80™ integrated) Electronic Control
Unit (ECU) Variant: The EAC (EC-80 integrated) ECU
is supported by EC-80 Advanced only.

•

X3, Pin 8 Compressor Control Output from ABS8:
The EAC system drives the compressor solenoid
governor through connector X3, Pin 8. When the EAC
system energizes the compressor solenoid governor
with positive voltage, the compressor will be unloaded
and therefore, as a result, not building air pressure.
When the EAC system de-energizes the solenoid
governor, the compressor will be loaded and building
air pressure.

ADVANCED FEATURES
The EAC system provides advanced air system control
features.
•

Energy Savings: The EAC system may exploit
certain engine monitoring situations by allowing the
compressor to engage and charge the system, taking
advantage of otherwise wasted energy. This feature
may result in slight overcharging of the service system,
not to exceed 140 psi.

•

Performance Enhancements: The EAC system may
operate slightly different than a traditional pneumatic
charging system. Because the EAC system can
monitor the air system and vehicle use, it may not
always load and unload the compressor at the same
pressures. Additionally, the EAC system is also capable
of monitoring the health of the air dryer cartridge using
available vehicle data. If the EAC system determines
that excessive water is accumulating in the air dryer
cartridge, it may unload the compressor and initiate a
purge. This may happen at a system pressure level
lower than expected. After the interrupted charge is
complete, the system will automatically continue to
charge as normal and will purge again when maximum
pressure is reached.

•

Cartridge Lifetime Prediction (CLP): This feature
monitors the vehicle usage conditions and provides
an estimate of the health and remaining life. It also
provides DTCs when the estimated life falls below
certain threshold levels. Bendix ® ACom ® PRO ™
Diagnostic Software supports the resetting of the CLP
to 100% remaining after servicing and replacing the
cartridge.

•

Diagnostics: The EAC system includes several
different diagnostic features that can provide DTCs
when abnormal system usage is suspected. This may
include excessive compressor usage or excessive
moisture build-up in the desiccant cartridge or system.

ELECTRONIC AIR CONTROL (EAC) SYSTEM
DESCRIPTION WITH BASIC GOVERNOR AND
ADVANCED FEATURES
The EAC system provides basic governor control and
advanced air system control features.
BASIC GOVERNOR CONTROL
The EAC system provides basic governor control and
loads/unloads the compressor to maintain a safe air system
pressure level. When the air pressure drops below the
cut-in pressure threshold, the EAC system will load the
compressor; when the air pressure is greater than the
cut-out pressure threshold, the EAC system will unload the
compressor and purge the air dryer desiccant to remove
moisture.

3

TROUBLESHOOTING
The Electronic Air Control (EAC) system normally operates
in the basic governor mode as described above loading
at cut-in and unloading (and regeneration) at cut-out air
pressures. If there are fault conditions and/or vehicle or
solenoid governor interface problems, normal operation
and advanced features may be disrupted. In this case,
check for the following abnormal conditions:

• Check the Vehicle J1939 CAN Connection and
Baud Rate: The EAC system requires vehicle CAN
messages and signal information that controls
the compressor. Check the vehicle J1939 CAN
bus connections to the EAC system. Vehicle
J1939 CAN_H should be connected to EAC X1,
Pin 8, and CAN_L should be connected to EAC
X1, Pin 7. The EC-80 is factory-programmed to
operate at baud rate 250kB (standard) and 500 kB
(optional). Check to ensure the vehicle CAN and
EC-80 baud rates match.

CONSTANT AIR BUILD: In certain fault conditions (i.e.
the solenoid is not working properly or the air dryer is
not properly connected), the EAC fail safe operation is
to constantly load the compressor building air pressure.
This condition will exist if there are compressor solenoid
governor connection problems or missing or invalid
vehicle CAN messages or signals.

UNEXPECTED DIFFERENCE IN CUT-IN AND CUTOUT: The EAC system has advanced features that will
temporarily adjust the normal cut-in and cut-out pressure
thresholds.

• Check the compressor solenoid governor: The
EAC system controls the compressor with a pneumatic
solenoid. Check the connection from the Bendix®
EC-80™, connector X3, Pin 8 to the solenoid (this is
the high side or positive voltage to Pin 1 of the two-pin
solenoid connector). Also, check the chassis ground
connection to Pin 2 of the two-pin solenoid connector.
When the primary or secondary air pressure is below
cut-in, Pin 1 to the solenoid should be low or ground
potential voltage to load the compressor. When the
primary and secondary air pressures are above cutout, Pin 1 to the solenoid should be high or positive
potential voltage to unload the compressor.
• Tank pressure: If the primary and secondary
tank pressure difference is more than 14 psi, the
compressor may enter a state of constant air build.
• Invalid primary or secondary pressure signal on
CAN: The primary and secondary pressure signals
are sent to the EAC controller over CAN, originating
from the vehicle system pressure sensors. During
normal operation and when the service system is
above cut-in pressure, these two (2) pressure signals
should be approximately equal. If the pressure signals
differ by more than one (1) bar (14.7 psi), the EAC
system can no longer trust the signal information
and may default to constant build of air. Check the
values of these signals per the vehicle manufacturer's
recommendation and replace if necessary.

4

• Overrun (OVR): When the vehicle is going downhill,
for example, the OVR feature will temporarily raise
the cut-in and cut-out pressures. Refer to the OVR
section within the EAC System Description with Basic
Governor and Advanced Features.
• Overtake (OVT): When there is high engine torque
demand, the OVT feature will temporarily lower
the cut-in and cut-out pressures. Refer to the OVT
section within the EAC System Description with Basic
Governor and Advanced Features.
EAC FAIL SAFE, DEFAULT OPERATION: Under
certain operating conditions, the EAC system will go into
the EAC fail safe default operation: Continuous Load,
Building Air. These conditions are:
• Loss of CAN: No CAN communication.
• Loss of AIR1 Message: CAN communication is
present, but there is no AIR1 message pressure
information.
• Pressure Implausibility: The difference between
primary and secondary pressure is beyond a threshold
parameter.

ELECTRONIC AIR CONTROL (EAC) SYSTEM
DEFAULT OPERATION AND SERVICE SHOP
INSTRUCTIONS
• Loaded Mode: The EAC system stays in loaded
mode, continuously building air; the Pressure Relief
Valve (PRV) will activate at overpressure.
• Cartridge Monitoring: The EAC system continues
to track air dryer cartridge health and will report
associated Diagnostic Trouble Codes (DTCs).
• Service Shop: The service shop should be aware
that if vehicle conditions put the EAC system
into continuous load operation, the PRV can be
compromised and the air dryer cartridge can become
saturated. In this case, the service person should
replace the PRV. The service person should also
check for EAC system mid- and high-level wetness
DTCs. If a high-level DTC exists, the air dryer
cartridge should be replaced. Refer to SD-08-12046,
Bendix ® AD-HF ® and AD-HFi™ Service Data Sheet,
on b2bendix.com.

EAC SYSTEM DIAGNOSTIC SUPPORT
DTC DETECTION
The EAC system contains self-testing diagnostic circuitry
that continuously checks for proper operation and external
compressor solenoid governor and wiring.

DTC DESCRIPTION AND REPAIR INFORMATION
The EAC (Bendix® EC-80™ integrated) Electronic Control
Unit (ECU) DTCs are supported with Bendix® ACom® PRO™
Diagnostic Software. Refer to Table 1.
Depending on the version of Bendix ® ACom ® PRO ™
Diagnostic Software, it will display the EAC (EC-80
Integrated) ECU on its roll call and other relevant screens
as either "Bendix EC-80 EAC" or "Electronic Air Control
(EC-80 integrated)."

5

ELECTRONIC AIR CONTROL (EAC) (BENDIX ® EC-80™ INTEGRATED) ELECTRONIC
CONTROL UNIT (ECU) DIAGNOSTIC TROUBLE CODES (DTCS) AND SERVICE
INFORMATION
SPN

FMI

DTC/Lookup
Code

Description

Service Shop Information

629

12

Controller operational defect.

Replace the Antilock Braking System
(ABS) Electronic Control Unit (ECU).

8621

13

Electronic Air Control (EAC)
memory error.

Replace or reprogram the ABS ECU.

1351

3

32-3

Bendix® AD-HFi™ Air Dryer
Inspect the AD-HFi air dryer solenoid
solenoid voltage above normal, or Pin 1 for short to voltage source.
shorted to high source.
See Figure 2.

1351

4

32-4

AD-HFi air dryer solenoid voltage
below normal, or shorted to low
source.

Inspect the AD-HFi solenoid Pin 1 for
short to ground potential. See Figure 2.

1351

5

32-1

AD-HFi solenoid current below
normal or open circuit.

Inspect the AD-HFi air dryer solenoid Pin 1
and Pin 2, wiring for open or disconnected