WORKHORSE CUSTOM CHASSIS
Service Manual
Automatic Transmission – Allison
2007 W Series
© 2006 Workhorse Custom Chassis — All Rights Reserved
SECTION
7.2
PAGE
219
2007 W Series Chassis
WSM082106
DTC P0742
Circuit Description
The transmission control module (TCM) uses data from
the engine speed sensor and the turbine speed sensor
to calculate the torque converter slip value. The TCM
then compares this calculated slip value to a preset
value in the TCM calibration.
DTC P0742 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
• DTC P0742 Torque Converter Clutch (TCC) System -
Stuck On
Conditions for Running the DTC
• DTC P0122, P0123, P0716, P0717, P0721, P0722,
P0743 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 transmission must be in a forward range.
• The torque converter clutch (TCC) is not enabled or
requested.
Conditions for Setting the DTC
DTC P0742 sets when the TCM detects TCC slip speed values
indicating a stuck on or locked condition for 2.5 seconds.
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.
• If failure occurs before shifting is completed, the
transmission will shift to NEUTRAL. If failure occurs
while shifting is being completed, the transmission will
shift to NEUTRAL or 1st range while diagnostic response
is active.
• If the shift selector is moved to NEUTRAL, the
transmission will shift to NEUTRAL.
• If the shift selector is moved to REVERSE, the
transmission will shift to NEUTRAL or REVERSE.
• If the shift selector is returned to DRIVE, the
transmission will shift to NEUTRAL or 1st range.
• DTC P0742 is stored in TCM history.
• The TCM inhibits TCC engagement.
• The TCM freezes shift adapts.
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
– A damaged terminal
