8
Trailer ABS Component Overview
Bendix
®
A-18
™
trailer ABS system includes the following
components:
•
Electronic Control Unit (ECU): The ECU monitors
wheel speeds and controls the trailer ABS valves. It
also diagnoses ABS malfunctions and stores failure-
specific fault codes. The ECU is usually attached to a
relay valve with a mounting bracket. The ECU may
also be directly frame mounted. One ECU can monitor
either two or four speed sensors and control either one
or two relay valves. If necessary more than one ECU
may be used on a single trailer.
•
Relay Valve: This component regulates brake chamber
air pressure. It houses the hold and release solenoids.
Each relay valve can control either two or four brake
chambers on an ABS equipped trailer. A relay valve
can have the ECU mounted to it (valve A in the
installation diagrams) or be a stand alone relay valve
(valve B in the installation diagrams) that is controlled
remotely by the ECU mounted on valve A.
•
Trailer Mounted ABS Warning Lamp: This indicator
lamp, located on the “Road Side” near the rear of the
trailer, warns the driver of ABS malfunctions (steady
“ON”). It is also capable of blinking diagnostic fault
codes.
•
Cab Mounted ABS Warning Lamp: This indicator
lamp, located on the driver instrument panel, also warns
the driver of ABS malfunctions. It is not capable of
blinking diagnostic fault codes.
•
Wheel End Speed Sensor and Tone Wheel: Single
point variable reluctance (magnetic) sensor that
generates an alternating current signal in response to
the movement of teeth on a tone wheel. The signal is
interpreted by the ECU to monitor wheel speed.
•
Diagnostic Port Connector: The diagnostic port
connector is an industry standard connector which is
used to provide a connection to the J1587 diagnostic
link. This connector also provides power and ground
for diagnostic test equipment.
•
Gladhand: The gladhands used on the ABS system
are the same as those used on non-ABS trailers.
•
Seven Way Main Electrical Connector: The seven
way receptacle is the same as those used on non-ABS
systems. This receptacle provides full-time power,
backup power via the brake light switch and ground for
the ABS electrical system.
•
Optional ISO 3731 connector: This is a 7-pin
connector similar to the J560 connector. The most
noticeable difference is that the ground terminal has a
gender opposite that of the other terminals. The primary
use for ISO 3731 is for the lighting connections on
European trailers. However, this connector is used to
provide interface to trailer ABS in some U.S.
applications. (In Europe another connector designated
as ISO 7638 is used to provide interface to the trailer
braking system.)
