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Section 3
ABS Questions and Answers
Section 3ABS Questions and Answers
The Electronic Control
Unit (ECU)
How do you activate the ECU?
In a constant-powered system, the ECU activates
and then begins a self-diagnostic check of the
system when you turn the ignition
ON
. In a
stoplight-powered system, the ECU activates when
you apply the brakes. All trailers manufactured on
or after March 1, 1998 will be equipped with ABS
that has constant power capability with stoplight
power as back-up.
What if the ECU finds a fault in an ABS component
during normal operation?
If the ECU senses a fault in the system (with an
ABS valve, for example), the ECU turns the trailer
ABS warning lamp on and returns the wheel
controlled by that valve to standard braking. Or, if
the ECU finds a fault with one wheel speed sensor
in a system that has four sensors on a tandem
axle, the ECU uses information from the other
sensor on the same side of the tandem to ensure
continuous ABS function. The ECU continues to
provide full ABS function to the wheels unaffected
by system faults. However, the ECU will turn the
trailer ABS warning lamp on to tell the driver a
fault has been detected in the system.
How does the ECU respond to a wheel
approaching lock-up?
The ECU directs the ABS relay valve to function as
a modulator valve and adjust air pressure to the
chambers up to five times a second. This pressure
adjustment allows a wheel (or wheels) to rotate
without locking.
The ABS Warning Lamp
What is the function of the warning lamp?
The warning lamp enables a driver to monitor the
ABS at all times. Refer to the OEM operating
manual for the mounting location of the
warning lamp.
How does the warning lamp operate?
How the warning lamp operates depends on
whether the ABS is powered by stoplight or
constant power:
앫
If the trailer was manufactured prior to February
28, 1998, or was manufactured outside of the
United States, the ABS may be either stoplight
or constant powered.
앫
If the trailer was manufactured March 1, 1998 or
later — and was manufactured in the United
States — it will have constant power capability.
This is mandated by Federal Motor Vehicle
Safety Standard (FMVSS) 121.
Check your vehicle specification sheet to
determine the type of ABS power.
Table B —
Stoplight Power
and
Table C — Constant Power
,
in this section, illustrate warning lamp operation
on stoplight and constant powered
ABS systems.
Table B — Stoplight Power
System Power Comes from Activating the Stoplight Circuit.
Brakes
Fault in System Vehicle Speed
Warning Lamp
Released
N.A.
N.A.
OFF
Applied
NO
Less than 4 mph
ON
for 3 seconds, then goes
OFF.
Applied
NO
Greater than 4 mph
Flashes once, then stays
OFF
for
remainder of stop.
Applied
YES
N.A.
ON
Summary of Contents for Easy-Stop Basic
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