PREVOST X3-45 Multiplex, Maintenance Manual

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8
REVISED 5/31/05
WARNING: The ABS off-road mode should not be
used on normal, paved road surfaces because vehicle
stability and steerability may be reduced. The ABS
Indicator Lamp will flash slowly to indicate to the driver
that the ABS off-road mode is engaged.
CAUTION: When ABS off-road mode is engaged,
stability functions are disabled at speeds below
approximately 25 mph. The ATC/ESP dash lamp will
illuminate to indicate to the driver that the stability
system is disabled.
The vehicle manufacturer should provide the optional ABS
off-road function only for vehicles that operate on unpaved
surfaces or that are used in off-road applications, and is
responsible for insuring that vehicles equipped with the ABS
off-road function meet all FMVSS-121 requirements and
have adequate operator indicators and instructions.
The vehicle operator activates the off-road function with a
switch on the dash panel. A flashing ABS Indicator Lamp
indicates to the driver that the ABS off-road function is
engaged. To exit the ABS off-road mode, depress and
release the switch. A new ignition cycle will also cause the
ECU to exit the ABS off-road mode.
All-Wheel Drive (AWD) Vehicles
AWD vehicles with an engaged interaxle differential (steer
axle to rear axle)/AWD transfer case may have negative
effects on ABS performance. Optimum ABS performance
is achieved when the lockable differentials are disengaged,
allowing individual wheel control.
Advanced EC-60
™
controllers can be programmed
specifically for this configuration to control the differential
lock/unlock solenoid in the AWD transfer case. When
programmed to do so, the ECU will disengage the locked
interaxle/AWD transfer case during an ABS event and
reengage it once the ABS event has ended.
ATC OPERATION
ATC Functional Overview
Just as ABS improves vehicle stability during braking,
ATC improves vehicle stability and traction during vehicle
acceleration. The EC-60
™
controller ATC function uses
the same wheel speed information and modulator control
as the ABS function. The EC-60
™
controller detects
excessive drive wheel speed, compares the speed to the
front, nondriven wheels, and reacts to help bring the wheel
spin under control. The controller can be configured to use
engine torque limiting and/or differential braking to control
wheel spin. For optimal ATC performance, both methods
are recommended.
ATC/ESP Lamp Output/ATC Mud/Snow Switch
Input
Advanced ECUs control the ATC/ESP dash lamp as
follows.
The ATC/ESP dash lamp illuminates:
1. During power up (e.g. when the vehicle is started) for
approximately 2.5 seconds and turns off after the self
test is completed, providing no diagnostic trouble codes
are present.
2. When ESP or ATC is disabled for any reason.
3. During an ESP or ATC event (the lamp will flash rapidly
at a rate of 2.5 per second).
4. When the ECU is placed in the ATC off-road mode
(the lamp will flash steadlily at a rate of once per 2.5
seconds). This notifies the vehicle operator that the
ATC Mud/Snow mode is active.
5. When the ECU is placed in the ABS off-road mode.
When in this mode, ESP will be disabled below 25 mph
and its inactive status will be indicated by a steadily
illuminated ATC/ESP lamp.
Differential Braking
Differential braking within ATC is automatically activated
when drive wheel(s) on one side of the vehicle are spinning
excessively, which typically occurs on road surfaces with
patches of ice. The traction system will then lightly apply the
brake to the drive wheel(s) that are spinning excessively.
The vehicle differential will then drive the wheels on the
other side of the vehicle.
Differential braking as part of ATC functionality is available
at vehicle speeds up to 25 MPH.
Disabling ATC Differential Braking
ATC differential braking is disabled under the following
conditions:
1. During power up (e.g. when the vehicle is started), until
the ECU detects a service brake application.
2. If the ECU receives a J1939 message indicating that
the vehicle is parked.
3. When the dynamometer test mode is active. The
dynamometer test mode is entered using the diagnostic
blink code switch or by using a diagnostic tool (such as
Bendix
®
ACom
™
Diagnostics).
4. In response to a serial communications request from
a diagnostic tool.
5. If "ATC Differential Braking" function is activated for a
long time period to avoid overheating of the brakes,
it would take approximately 3 continuous minutes of
activation for the timeout to occur. Once timed out,
approixmately 2 minutes of "cool off" time would be
required before ATC Differential Braking can be used
again.
6. When certain diagnostic trouble code conditions are
detected.
Engine Torque Limiting with Smart ATC
™
Traction Control
The EC-60
™
controller uses Engine Torque Limiting to
control drive axle wheel slip. This is communicated to the
engine control module (using J1939), and is available at
all vehicle speeds.