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MBS-1P Installation
ABS System Diagnostics
Initial System Checkout
When the system is first powered up, the ABS malfunction lamp will come
ON for two seconds then go OFF, indicating the system has passed all
self-tests. All MBS-1P units must pass operation checks before the trailer is
placed in service.
Pneumatic Diagnostics
The Wabash ABS system does not monitor the air system of the vehicle. For
example, if there is an air leak, kink in the line, or faulty relay valve, the ABS
malfunction lamp will not show a fault in the system. However, if a malfunction
in the air system arises and it cannot be determined if the ABS valve is
causing the problem, the ABS can simply be bypassed using a short length of
airline and two push-in unions. For example, if an unknown kink exists in the
control line and the brakes will not apply, simply remove the airlines from the
quick connect fittings on the ABS valve and insert the short length of airline
using the push-in unions. The system can then be reexamined without the
ABS affecting the system. If the brakes still do not apply it can then be
assumed that the ABS valve is not causing the problem.
Electrical Diagnostics
The malfunction lamp is an important tool when assessing the status of the ABS
system. When the system is operating properly the malfunction lamp will
illuminate briefly, then go OFF every time the system is powered up. If the vehicle
is stationary at power up, the lamp will remain ON for two seconds and the PCM
will perform a functional test causing an audible clicking or puffing. If the vehicle is
mobile at power up, the lamp will remain ON for one second and the PCM
self-test will be aborted. The PCM self-test is performed at each stationary power
up to give the operator an audible sign that everything is performing normally.
The ABS system receives power from the stop lamp circuit (pin 4 of J560
connector – red) and the auxiliary circuit (pin 7 of J560 connector – blue).
This means the system will operate on a tractor with or without the auxiliary
circuit powered at tractor ignition. In a situation where the system only
receives power from the stop circuit, the malfunction lamp will illuminate briefly
each time the brakes are applied and the PCM self test will be performed at
each stationary brake application.
Upon power up, if the system behaves differently than described above,
such as the malfunction lamp remains illuminated or does not come ON
at all, follow the instructions in the next section to determine the cause of
the problem.
