WORKHORSE CUSTOM CHASSIS
Service Manual
Automatic Transmission – Allison
2007 W Series
© 2006 Workhorse Custom Chassis — All Rights Reserved
SECTION
7.2
PAGE
185
2007 W Series Chassis
WSM082106
DTC P0726
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 P0726 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
• DTC P0726 Engine Speed Sensor Circuit Performance
Conditions for Running the DTC
• DTC P0716, P0717 and P0727 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.
• The input speed is greater than 600 RPM for 1.0 second.
Conditions for Setting the DTC
DTC P0726 sets when the TCM detects a large unrealistic engine
speed or if excessive noise is present in the engine speed sensor
circuit.
Action Taken When the DTC Sets
• The TCM illuminates the malfunction indicator lamp
(MIL) during the second consecutive trip in which the
Conditions for Setting the DTC are met.
• DTC P0726 is stored in TCM history.
• The TCM freezes shift adapts.
• The TCM inhibits torque converter clutch (TCC)
engagement.
Conditions for Clearing the DTC
A scan tool can clear the code from TCM history. The
TCM automatically clears the DTC from TCM history if
the vehicle completes 40 warm-up cycles without failure.
Diagnostic Aids
• Inspect the wiring for poor electrical connections at the
TCM. Inspect for the following conditions:
– A bent terminal
– A backed-out terminal
