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 governor
control, J1939 messaging, Diagnostic Trouble Codes
(DTCs), and advanced functionality.

DESCRIPTION
ELECTRONIC AIR CONTROL (EAC) SYSTEM
The EAC system adds intelligent electronic air control of
the solenoid governor that will load and unload the air
compressor. The EAC system provides the basic governor
operation to maintain 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 ® 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

AD-HFi
Solenoid
Governor

GND

Figure 1 – EAC System Diagram
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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).

•

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 ESP® only.

•

X3, Pin 8 Compressor Control Output from ABS8:
The EAC system drives the solenoid governor
through connector X3, Pin 8. When the EAC system
energizes the 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. See Figure 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
solenoid governor to maintain air pressure levels. The
EAC (EC-80 integrated) ECU monitors the air system
pressure. The unit energizes and de-energizes the
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® Diagnostic
Software to evaluate system status.
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. The solenoid governor, which
is part of the air dryer, is controlled by the EAC ECU
to load and unload the air compressor.

PIN 2
NEGATIVE

SOLENOID
COIL

1N4004
DIODE

PIN 1
POSITIVE
PIN 1
POSITIVE TO EC-80
X3, PIN 8

AD-HFi SOLENOID
GOVERNOR
CONNECTOR PIN OUT

PIN 2
NEGATIVE TO
CHASSIS GROUND

Figure 2 – Solenoid Governor Pin Out

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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 through
the solenoid governor attached to the air dryer and
loads/unloads the compressor to maintain 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.

This information may be available via the vehicle dash
interface or via Bendix ACom Diagnostic software.
This may help customers predict a consistent
maintenance interval for the air dryer cartridge on the
vehicle. However, the cartridge change interval should
NOT exceed the recommended intervals provided
in BW8068, Recommended Cartridge Maintenance
Intervals for Bendix Air Dryers, on B2Bendix.com.

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. Refer to BW8068, Recommended
Cartridge Maintenance Intervals for Bendix Air
Dryers, on B2Bendix.com for recommended cartridge
replacement information.

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Cartridge Lifetime Prediction (CLP): This feature
provides additional maintenance diagnostic information
for the cartridge based on air usage and vehicle
performance including an estimate of the health and
remaining life of the cartridge. It also provides DTCs
when the estimated life falls below certain threshold
levels. Bendix® ACom® 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.

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:
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 solenoid governor
connection problems or missing or invalid vehicle CAN
messages or signals.
• Check the solenoid governor: The EAC system
controls the compressor through the solenoid
governor on the Bendix® AD-HFi® air dryer. 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 cut-out, 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.

• 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.

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.
• Overrun (OVR): When the vehicle is going downhill,
for example, the OVR feature will temporarily raise
the cut-in and cut-out pressures.
• Overtake (OVT): When there is high engine torque
demand, the OVT feature will temporarily lower the
cut-in and cut-out pressures.
• Interrupted Charge Regeneration (ICR): When the
air dryer cartridge moisture level begins to approach
oversaturation for a single charge cycle, the ICR
feature will temporarily unload the compressor
to initiate an air dryer purge. After this purge has
completed, the charge cycle will continue again until
cut-out pressure is achieved.
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.

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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, a qualified service technician
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.

BENDIX TECHNICAL ASSISTANCE TEAM
For direct telephone technical support, the Bendix
Te c h Te a m i s a v a i l a b l e a t 1 - 8 0 0 - A I R - B R A K E
(1-800-247-2725), Monday through Thursday, 8:00 a.m.
to 6:00 p.m. and Friday, 8:00 a.m. to 5:00 p.m. ET.
Follow the instructions in the recorded message. The
Bendix Tech Team can also be reached by email at
techteam@bendix.com.
ABBREVIATIONS AND DEFINITIONS
ABS

Antilock Braking System

AD-HFi
EP

Air Dryer - High Flow Intelligent with
Solenoid Governor, Extended Purge Tank

AD-HFi
SP

Air Dryer - High Flow Intelligent with
Solenoid Governor, Standard Purge Tank

ATC

Automatic Traction Control

BCVS

Bendix Commercial Vehicle Systems LLC

CAN

Controller Area Network

Cut-In

The lower air pressure threshold at which
the compressor loads to build pressure

Cut-Out

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

The higher air pressure threshold at which
the compressor unloads to stop building
pressure

DTC

Diagnostic Trouble Code

EAC

Electronic Air Control

BENDIX ACOM DIAGNOSTIC SOFTWARE

ECM

Electronic Control Module

The EAC system is supported by Bendix® ACom® Diagnostic
Software. Visit B2Bendix.com for additional information and
for downloads of the ACom Diagnostic Software.

ECU

Electronic Control Unit

ESP

Electronic Stability Program

GND

Electrical Ground Potential

ICR

Interrupted Charge Regeneration Feature

OVR

Overrun Feature

OVT

Overtake Feature

PRV

Pressure Relief Valve

SA

Source Address

Solenoid
Governor

The part of the AD-HFi air dryer that is
controlled by the EAC ECU to load and
unload the air compressor, and purge the
air dryer.

EAC SYSTEM DIAGNOSTIC SUPPORT
DTC DETECTION

DTC DESCRIPTION AND REPAIR INFORMATION
The EAC (Bendix® EC-80™ integrated) Electronic Control
Unit (ECU) DTCs are supported with Bendix ACom
Diagnostic Software.
Bendix ACom Diagnostic Software supports all DTCs for
Bendix products. For additional troubleshooting support,
go to B2Bendix.com > Services & Support > Diagnostic
Trouble Code Search.
DIAGNOSTIC TROUBLE CODE (DTC) STORAGE /
EVENT HISTORY
The Electronic Air Control (EAC) system and Bendix ACom
Diagnostic Software retain a record of all DTCs. This record
is commonly referred to as "event history." When a DTC
self heals or is manually cleared, the DTC code remains
in event history as an inactive DTC.

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Table 1 – Abbreviations and Definitions

2-4
COMPRESSOR
UNLOADER
(1/4-in. NPT)

TO ECU
P5 EXTERNAL FILL (1/4-in. NPT)

21 PRIMARY
(1/4-in. NPT)
1A SUPPLY
(1/4-in. NPT)
1 SUPPLY
(1/2-in. NPT)

22 SECONDARY
(1/4-in. NPT)

23 AUXILIARY 2
(1/4-in. NPT)

3 PURGE

24 AUXILIARY 1
(1/4-in. NPT)
STANDARD SYMBOL ISO 1219

Figure 3 – Schematic
RELATED DOCUMENTATION
Bendix Specifications
SD-08-12046

Bendix® AD-HF® and AD-HFi® PuraGuard® Oil Coalescing Air Dryer Service Data Sheet

SD-13-4986

Bendix® ESP EC-80™ Controller Service Data Sheet

BW8068

Recommended Cartridge Maintenance Intervals for Bendix® Air Dryers
Society of Automotive Engineers (SAE) Documents

SAE J1939-71

Vehicle Application Layer
Government Requirements

FMVSS 121

U.S. Department of Transportation, National Highway Safety Administration Federal Motor Vehicle Safey
Standard 571.121
Other Documentation

RP-1210A

Technology Maintenance Council (TMC) Recommended Practice for Microsoft® Windows® communications
APO

Table 2 – Related Documentation

Any references in this document to MICROSOFT, WINDOWS, and any other company or trademark are solely for
identification and cross reference purposes. The trademarks are the property of their respective companies.
Unless otherwise indicated, the trademarks used in this document, including Bendix, are United States
trademarks owned by, or licensed to, Bendix Commercial Vehicle Systems LLC.
SD-08-12000 Rev 002 © 9/2025 Bendix Commercial Vehicle Systems LLC, a member of Knorr-Bremse • All Rights Reserved

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