Table of Contents
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Section 1
Organization of This Manual
Introduction
The manual covers the following subjects.
Height Control System Operation — This section
describes the theory of operation and features of
the system. It also discusses fault tolerance and
fallback operating modes.
Height Control System Components — This
section shows pictorial views of the components
and their associated part numbers.
Height Control System Configurations — This
section shows the available system configurations
as installed on typical vehicles.
Diagnostics — This section discusses available
service tools, retrieval of fault codes and proce-
dures to follow if system operation is abnormal, but
fault codes are not available.
Troubleshooting — This section discusses proce-
dures to follow to determine the cause of malfunc-
tions based on fault code information or other
indications.
Service and Repair Procedures — This section
provides the procedures for removal and replace-
ment of failed components.
Suspension Height Control Operation
The suspension height control system has the fol-
lowing functionality.
•
The controller receives a command height set-
ting from the operator interface. This command
may be sent via the J1939 data link or alterna-
tively as a variable input voltage to the Mobility
Mode Signal pin of the control unit (Pin 7).
•
There are height control sensors mounted at
each corner of the vehicle. The height sensors
are either directly connected to the suspension
control unit, or indirectly connected via J1939
from an active dampening system. The control-
ler adjusts the pressure in the suspension air
bags, so that the height sensor readings match
the command height; for example, the height
that the chassis sets above the bump stops.
•
The controller also monitors the air bag pres-
sure and uses this information along with a
vehicle specific calibration table to provide load
information.
Meritor Maintenance Manual MM-0997 (Revised 12-09)
•
The controller contains logic whereby the sys-
tem will not activate unless the reservoir has a
minimum level of pressure available, and the
system voltage is within a range whereby the
solenoids within the controller can be reliably
activated.
Fault Tolerance and Fallback Modes
The controller monitors the system I/O and is capa-
ble of implementing a variety of fallback modes in
response to failures. The controller will also log
diagnostic codes to support vehicle troubleshoot-
ing and service.
•
Loss of Power to Ignition Input — The sus-
pension height control system will be inopera-
tive in this case.
•
Loss of Battery Power — This fault condition
will be logged, and an error code transmitted
via J1939. For currently available systems, this
will result in an inoperative control system. (A
change is underway, whereby the system will
revert to dependence on the ignition signal as
a fallback. In this case, operation will be nor-
mal, although the fault condition will be logged
and reported.)
•
Sensor Failures — If height position informa-
tion is not available due to an individual sensor
failure, the controller will log and report the fail-
ure via J1939. As a fallback, the controller will
use the information from the opposite side sen-
sor for height information, and use the internal
manifold pressure sensor to equalize pressure
in the air bags side-to-side.
•
Air Bag Puncture — If the control unit is not
able to generate pressure at a controlled air
bag within a reasonable time, a fault will be
logged, and that channel will be isolated. (Sev-
eral air bags may be connected in parallel at a
vehicle corner.) Note: There are configurations
where each of the air bags at a corner is con-
nected to a separate channel. However, it is
more common to have air bags connected
directly in parallel. Because of the need to both
raise and lower pressure, no isolation is possi-
ble, and the collection of air bags is treated as
a single unit in this case.
•
Solenoid or Solenoid Driver Failure, Inlet
Solenoid — If this solenoid fails, a fault will be
logged and transmitted via J1939. The system
will be unable to inflate air bags, but will be
able to deflate them.
Introduction
Page 3
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Table of Contents
Troubleshooting
