2
Stability and Safety Enhancement Systems
11
WABCO
Maintenance Manual MM-0112 (Revised 07-18)
Figure 2.9
Hill Start Aid (HSA)
Hill Start Aid (HSA) supports select automated manual transmissions
in reducing/totally eliminating the rolling back of the vehicle while
launching on a grade. When requested from the transmission, HSA
holds pressure in the service brakes of all axles of the towing vehicle
when the vehicle is standing still. HSA will hold pressure for a
maximum of three seconds following full release of the brake pedal.
Communication between the transmission and the ECU takes place
via the J1939 data link.
HSA grade threshold parameters may be modified in the
Transmission ECU. These parameters must be reviewed with the
transmission manufacturer prior to making any modifications in
order to ensure safe operation.
HSA Components
HSA is available on ABS ECUs with E4.4 software revision or higher.
Same as ESC, HSA is built from the ABS platform and uses many of
the same components as ATC and RSC. HSA uses the front axle
active braking valve as well as the rear active braking valve to help
maintain the pressure trapped during HSA activation.
A pressure sensor provides the system with the driver’s brake
demand. The measured pressure is used by HSA to set the trapped
pressure and/or activate the HSA function.
The vehicle manufacturer can provide an HSA switch multiplexed
through the dashboard or hard wired for momentary HSA
deactivation.
An HSA lamp, either hard wired or multiplexed, provides the driver
with a visual indication of system deactivation and/or active fault. If
the lamp is hard wired, it must be an incandescent lamp or LED with
a resistor to prevent the ECU from setting a fault code.
A failure detected on any of these components will lead to no HSA
availability. To troubleshoot the HSA, refer to Section 3 –
Diagnostics, Troubleshooting and Testing.
Figure 2.9
4007814
a
VALVE PACKAGE
INSTALLATION (REAR)
AIR LINES
ELECTRICAL LINES
4
S/
4
M ESC/ATC
(ALSO AVAILABLE IN
6S CONFIGURATIONS)
ESC
MODULE
LAMPS
TRAILER ACTIVE
BRAKING
VALVE
TRAILER STABILITY
CONTROL
MODULATOR
(OPTIONAL)
PRESSURE
SENSOR
ATC VALVE
SAS
FRONT AXLE
ACTIVE
BRAKING
VALVE
TRACTOR
PROTECTION
VALVE
