Section 3
ABS Questions and Answers
Page 8
Table C — Constant Power
An ECU with part number 472 500 001 0
manufactured prior to September 1997 requires all
sensed wheels to detect a 4 mph signal to shut off
the ABS warning lamp. Do not confuse this with a
faulty ABS system. If the warning lamp stays on
when the brakes are applied to a moving vehicle,
service the ABS system.
Most trailers manufactured prior to February 1998
require that the brakes be applied to operate the
ABS warning lamp. If the warning lamp stays on
when the brakes are applied to a moving vehicle,
service the ABS system.
What does the trailer ABS warning lamp mean to
service personnel?
The trailer ABS warning lamp indicates the status
of the trailer ABS. If it comes ON and stays ON
when you apply the brakes to a moving vehicle,
there is an ABS malfunction. It is normal for the
lamp to come ON and go OFF to perform a bulb
check, but it should not stay ON when the vehicle
is moving above 4 mph. As with any safety system,
it is important not to ignore this warning. If the
warning lamp indicates a malfunction, the vehicle
can be operated to complete the trip, but it is
important to have it serviced as soon as possible
using the appropriate maintenance manual to
ensure proper braking performance and that the
benefits of ABS remain available to your drivers.
Typical ABS warning lamp mounting locations are
illustrated in Figure 3.1 .
For more information, contact WABCO North
America Customer Care at 855-228-3203.
System Is Powered When Ignition Is Switched ON.
Brakes Ignition Fault in System Vehicle Speed Warning Lamps (Trailer and Dash)
Released OFF N.A. N.A. OFF
Released ON NO Less than 4 mph ON for 3 seconds, then go OFF.
Released ON NO Greater than 4 mph OFF
Released ON YES N.A. ON
Applied OFF NO Less than 4 mph ON for 3 seconds, then go OFF.
Applied OFF NO Greater than 4 mph Flash once, then stay OFF for
remainder of stop.
Applied OFF YES N.A. ON
Applied ON NO Less than 4 mph ON for 3 seconds, then go OFF.
Applied ON NO Greater than 4 mph OFF
Applied ON YES N.A. ON
Figure 3.1
1 Prior to March 1, 1998
2 On or after March 1, 1998
Typical ABS Warning Lamp Mounting Locations
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