WORKHORSE CUSTOM CHASSIS
Service Manual
Automatic Transmission – Allison
2007 W Series
© 2006 Workhorse Custom Chassis — All Rights Reserved
SECTION
7.2
PAGE
181
2007 W Series Chassis
WSM082106
DTC P0722
Circuit Description
The speed sensors are variable reluctance devices
that convert mechanical motion to an AC voltage. Each
sensor consists of a wire coil wrapped around a pole
piece that is adjacent to a permanent magnet. These
elements are contained in a housing that is mounted
adjacent to a rotating ferrous member. 2 signal wires
extend from one end of the housing and an exposed
end of the pole piece is at the opposite end of the
housing. The permanent magnet produces lines of
fl ux around the pole piece. As a ferrous object, such
as a gear tooth, approaches and passes through the
gap at the end of the pole piece, an AC voltage pulse
is induced in the wire coil. The transmission control
module (TCM) calculates the frequency of these AC
pulses and converts it to a speed value. The AC voltage
generated varies from 150 m volts at low speed to 15
volts at high speed. The signal wires from the sensor are
formed as twisted pairs to cancel magnetically induced
fi elds. The cable is also shielded to protect from voltage
related fi elds. Using 2 wire differential inputs at the TCM
eliminates noise from other sources.
DTC P0722 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
• DTC P0722 Output Speed Sensor Circuit No Signal
Conditions for Running the DTC
• DTC P0716, P0717, P0721, P0731, P0732, P0733,
P0734, P0735, and P0736 are not active.
• The components are powered and ignition voltage is
greater than 9.0 volts and less than 18 volts.
• Engine speed is greater than 200 RPM and less than
7,500 RPM for 5 seconds.
• Turbine speed is greater than 1,050 RPM.
• The shift selector indicates a valid range selection.
Conditions for Setting the DTC
DTC P0722 sets when the TCM detects one of the following
conditions:
• An unrealistically large change in output speed
• An unrealistically low output speed
Action Taken When the DTC Sets
• The TCM illuminates the malfunction indicator lamp
(MIL).
• When failure occurs in a forward range and shifting
is complete, the transmission remains in the current
range. When failure occurs while in a forward range
and the shift is in process, the transmission returns to
the previous range, except in post-shift state, where the
transmission will continue to the commanded range.
When failure occurs in other conditions, the transmission
shifts to 1st, 3rd or 5th. While diagnostic response is
active, if the shift selector is moved to NEUTRAL or
REVERSE, or any other forward range, the transmission
will lock in NEUTRAL.
• DTC P0722 is stored in TCM history.
