Fault Code Guide

General Information
A PTO (power takeoff) and pump controls are op-
tions that can be ordered for a Business Class
®
M2
vehicle at the time the vehicle is ordered, after the
vehicle is delivered, or when buying a used vehicle.
A vehicle with a Mercedes-Benz AGS
1
transmission
must have PTO controls installed via the M2 electri-
cal system. This is because the AGS electronics re-
quire some messages to be broadcast to disengage
the clutch from the flywheel so that the PTO mecha-
nism can be engaged, and then to engage the clutch
on the flywheel after the PTO mechanism is en-
gaged. If the vehicle has a Mercedes-Benz AGS
transmission and is not equipped with PTO controls,
see Section 54.00, Subject 110, for instructions on
adding a feature.
A vehicle that is equipped with a transmission other
than a Mercedes-Benz AGS is not required to use
Freightliner PTO controls. PTO controls can be wired
around the Business Class M2 electronic controls.
A vehicle with an Allison automatic transmission and
body builder-installed PTO controls must have the
transmission controller’s PTO request input circuit
connected to the activation switch.
PTO and pump controls use low-current outputs and
digital inputs on the chassis module at the C5 electri-
cal connector.
Feedback from the PTO or pump mechanism is re-
quired for correct operation of the PTO and pump
controls. Feedback is provided by a ground input to
the chassis module. A grounded feedback circuit indi-
cates that the system is activated. An open feedback
circuit indicates that either the system is not acti-
vated (PTO switch is not turned on), or there is a
malfunction (PTO switch is turned on).
Definitions
Air shift PTO—Air pressure is used to shift the PTO
mechanism.
Hydraulic shift PTO—Hydraulic pressure is used to
shift the PTO mechanism. This is usually only avail-
able with an automatic transmission.
Normally closed AMU solenoid—Blocks the flow of
air until power is applied to the solenoid coil.
Normally open AMU solenoid—Allows air to flow
until power is applied to the solenoid coil.
Pump—Also called a split shaft PTO. The main
driveshaft is "split" by the PTO. The PTO is actually
a transfer case.
PTO Controls
The PTO controls include two types of electrical de-
signs. The controls for air shift PTOs drive an AMU
or AAVA solenoid. The controls for hydraulic shift
PTOs drive a relay. Hydraulic solenoids require about
1.5 amps of current to engage a PTO mechanism.
Pump Controls
The pump controls comprise a single electrical de-
sign. Two solenoid outputs are used to shift the
transfer case. One solenoid provides air when the
feature is activated (normally closed). The other sole-
noid turns off the air supply when the feature is de-
activated (normally open).
1
The AGS and AGS2 designations refer to the same Mercedes-Benz transmission. References to AGS2 may be found in ServiceLink
®
.
PTO and Pump Electrical Controls 54.38
General Information
Business Class M2 Workshop Manual, Supplement 22, September 2012 050/1