Fault Code Guide

amps. The 2010 CHM does not have the current
sourcing ability to drive these solenoids, so a relay in
the chassis PDM is added to the circuit. The ener-
gized solenoid opens and directs air flow by means
of a three-port valve. An open solenoid removes the
air supply to the rear suspension and vents the exist-
ing suspension pressure, allowing the rear of the ve-
hicle to be lowered.
Feedback from the suspension dump solenoid air
circuit is required for correct operation of the suspen-
sion dump controls. Feedback is provided by a
ground input to the CHM. The input is at ground
when a pressure switch within the AMU solenoid
closes. On AAVA-equipped vehicles, the pressure
switch is in the air line. A grounded feedback circuit
from the closed pressure switch indicates that the
system is activated. An open feedback circuit indi-
cates that the suspension dump is not activated (sus-
pension dump switch is not turned on), or there is a
malfunction (suspension dump switch is turned on
but the pressure switch is still open).
On a suspension dump with a lock solenoid, there is
a second normally open AMU/AAVA solenoid that
activates a double check valve in the rear suspen-
sion air supply. This valve keeps the rear suspension
in the last selected state when the engine is turned
off. This feature permits an override of the automatic
refill, allowing the suspension to stay lowered. The
lock solenoid receives power through a BHM-
supplied splice pack.
A remote-activation switch is commonly installed in
ambulances so that the suspension dump can be
activated when the rear door opens. Freightliner pro-
vides a circuit that the body builder uses to install a
remote-activation switch. The remote-activation
switch is usually located at the rear of the ambu-
lance. The remote-activation switch receives power
through a direct wiring connection to the BHM.
Fifth Wheel Slide
A sliding fifth wheel is an option on an M2 vehicle. A
sliding fifth wheel allows the weight of the trailer to
be transferred between the tractor axles, thereby in-
creasing or decreasing the distance between the
front of the trailer and the back of the cab. A sliding
fifth wheel can be adjusted to allow enough distance
between the trailer and the cab to prevent the trailer
from hitting the cab during a turn.
Fifth Wheel Slide Controls
With the engine running, the fifth wheel slide can be
activated using a momentary, two-position smart
switch. Pressing the upper half of the fifth wheel slide
switch activates the fifth wheel slide. Pressing the
upper half of the fifth wheel slide switch again deacti-
vates the fifth wheel slide. See Fig. 4. If the fifth
wheel slide is activated and the engine is turned off,
the system will deactivate the fifth wheel slide. Driv-
ers may activate the fifth wheel slide when vehicle
speeds are below 8 mph (13 km/h). The fifth wheel
slide automatically deactivates when the vehicle
reaches speeds greater than 10 mph (16 km/h).
When the fifth wheel slide switch is activated, the
CHM activates a low-current output to a normally
closed air management unit (AMU) solenoid. On
AAVA vehicles, the solenoid current is about 1.5
amps. The 2010 CHM does not have the current
sourcing ability to drive these solenoids, so a relay in
the chassis PDM is added to the circuit. The ener-
gized solenoid opens and supplies pressurized air to
an air cylinder located on the fifth wheel. The cylin-
der operates a mechanical linkage that moves two
plunger arms that are used to lock the fifth wheel in
position. The spring return plungers are located on
each rail of the fifth wheel mounting assembly. When
the air cylinder is pressurized, the plungers withdraw
and the fifth wheel is free to slide along the mounting
rails. When the fifth wheel slide is deactivated, the
springs on the linkage arms return the plungers to a
lock position on the rails. See Fig. 5.
Feedback from the fifth wheel slide air cylinder circuit
is required for correct operation of the fifth wheel
slide controls. Feedback is provided by a ground
input to the CHM. The ground input is delivered
when a pressure switch within the AMU solenoid
closes. On AAVA-equipped vehicles, the pressure
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02/15/2006
SLIDE
Fig. 4, Fifth Wheel Slide Switch
Chassis Electrical Control Systems 54.40
General Information
Business Class M2 Workshop Manual, Supplement 22, September 2012050/4