Bendix Commercial Vehicle Systems eTrac Automated Air Pressure Transfer System - Manual (Page 3)

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3. COMPONENTS See Figure 1.
The Bendix ® eTrac ™ system installation uses the following
components:
•
Electronic Control Unit (ECU): The specifically-
configured Bendix ® Premium, or Advanced, ABS ECU
monitors the speed sensor signals at each wheel-end
and during automatic traction control events under 25
MPH signals the Bendix ® FCS-9700 ™ Solenoid Valve
to close.
CAUTION: When replacing a Bendix eTrac-
enabled ECU, it is important to replace it ONLY with
another Bendix eTrac-enabled ECU as indicated by the
CAUTION label located on the ECU. Installation of a
non-eTrac-enabled ECU on an eTrac-equipped vehicle
can result in erroneous eTrac system interventions,
potentially causing vehicle damage and/or personal
injury.
CAUTION
Bendix ®
REPLACE ONLY WITH
CAUTION
ETRAC ENABLED ECU
REPLACE ONLY WITH ETRAC
REFERENCE BW2921
eTrac ™
ENABLED ECU
REFERENCE SD-13-21021
FIGURE 2 - EITHER BENDIX ® eTrac ™ SYSTEM CAUTION
LABEL MAY BE LOCATED ON THE ECU
• Dash-Mounted Mud/Snow Switch (Not shown.)
• Bendix FCS-9700 Solenoid Valve: Energized by the
ECU, this normally-open valve moves to the closed
position when the Bendix eTrac system is active (and
remains on five (5) seconds after the traction event
ends). See SD-03-10433 for more information about
this valve.
• Bendix ® R-12 ® Relay Valve: This is the “dump” valve
used for venting the Bendix eTrac system.
During the Normal Mode this relay valve is used to
provide an open channel for the inflation and deflation
of the tag axle suspension air bags (to maintain equal
pressure with the drive axle suspension air bags).
See Figure 3.
During the Bendix eTrac system Active Mode, the relay
valve isolates the rest of the air suspension system from
the tag axle suspension air bags and “dumps” the air
pressure from them. The air is exhausted through the
relay’s exhaust port. See Figure 4.
During the Pressure-Limiting Mode, the control port
of the “dump” valve receives air pressure from the
backfeed valve. This re-inflates the tag axle suspension
air bags as required. See Figure 5.
See SD-03-1064 for more information about this valve.
• Bendix ® DC-4 ® Double-Check Valve: This valve
toggles based on the higher supply pressure.
When in Normal Mode the double-check valve allows
the delivery from the solenoid valve to hold the tag axle
suspension air bags open to the same pressure as the
drive axle suspension air bags. See Figure 3.
In the Active Mode, the control air from the solenoid
valve to the “dump” valve ends, and the air is vented
back — through the double-check valve — and out of
the solenoid valve exhaust. See Figure 4.
During the Pressure-Limiting Mode, the double-check
valve allows air pressure from the backfeed valve to
the control port of the “dump” valve. This re-inflates
the tag axle suspension air bags as required.
See Figure 5.
See SD-03-2202 for more information about this valve.
• Bendix ® RV-3 ™ Valves: Typically used for pressure
reduction in air brake systems, this valve provides two
special functions: It operates as a backfeed valve,
and it also operates as a pressure-limiting valve. See
SD-03-3515 for general information about this valve.
NOTE: When replacing the valves used in this
system, it is important to replace ONLY like for like
part numbers (or direct replacement parts as verified
by Bendix.) In particular, the system upper pressure
limit for the drive axle suspension air bags is pre-
determined by the OEM, and this upper pressure limit
determines the specific Bendix RV‑3 valves that must
be used to avoid damage to the drive train.
NOTE: In the case of the valve used to backfeed the
Bendix eTrac system, it is necessary to install the valve
as shown in the system diagrams, and not to follow
the port designations (such as SUP for supply, etc.)
cast into the valve housings.