without the sensor information but at a reduced per-
formance level.
If a serious malfunction causes a total switch-off of
one or more electronic braking circuits, a pure pneu-
matic backup system is available.
The following functions can be deactivated in the
event of a malfunction:
•
ABS can be deactivated at one individual
wheel, at one axle, or for the whole vehicle.
•
ATC control can be deactivated. If it is shut
down, then both the brake control and the en-
gine control will be shut down.
•
If electrical control is lost, the affected axle is
braked by means of the pneumatic redundancy
pressure. The driver must compensate by ex-
erting more force on the brake pedal to stop
the vehicle.
This system has built-in diagnostics to ensure that all
components are operating properly. Under normal
conditions, the system performs a three second self-
check when the ignition is turned on. The two warn-
ing lamps (EBS, ABS) and the information lamp
(ATC) should illuminate for three seconds and then
go out if all EBS components are working properly. If
all three lamps do not switch on or if all three lamps
do not switch off after three seconds, the system
should be checked.
NOTE: If there is no bulb check and no dis-
played fault, most likely the brake pedal is par-
tially depressed, either by the driver or by some-
thing holding the pedal down. This safety
feature alerts the driver that the brake pedal is
not fully in the released position.
Automatic Slack Adjusters
Automatic slack adjusters are required on all vehicles
equipped with air brakes manufactured after October
20, 1994. Automatic slack adjusters should never be
manually adjusted except during routine maintenance
of the foundation brakes (e.g., replacing shoes), dur-
ing slack adjuster installation or in an emergency
situation.
When the brake pushrod stroke exceeds the legal
brake adjustment limit on a vehicle, there is likely a
mechanical problem with the foundation brake com-
ponents or the adjuster is improperly installed.
Visit a repair facility as soon as possible when
brakes equipped with automatic slack adjusters are
determined to be out of adjustment.
WARNING
Manually adjusting an automatic slack adjuster to
bring the pushrod stroke within legal limits is
likely masking a mechanical problem. Adjustment
is not repairing. In fact, continual adjustment of
automatic slack adjusters may result in prema-
ture wear of the adjuster itself. Further, the im-
proper adjustment of some automatic slack ad-
justers may cause internal damage to the
adjuster, thereby preventing it from properly
functioning.
Steering and Brake Systems
6.6