WORKHORSE CUSTOM CHASSIS
Service Manual
2007 W Series
SECTION
7.2
PAGE
206
Automatic Transmission – Allison
2007 W Series Chassis
© 2006 Workhorse Custom Chassis — All Rights Reserved
WSM082106
DTC P0734
Circuit Description
The transmission control module (TCM) uses input
from the turbine speed sensor and output speed
sensor (OSS) to determine gear ratios. The TCM then
compares the known gear ratio to the calculated gear
ratio for the current range.
DTC P0734 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
• DTC P0734 Incorrect 4th Gear Ratio
Conditions for Running the DTC
• DTCs P0716, P0717, P0721, P0722, P0875, and P0876
are not active.
• The components are powered and ignition voltage is
greater than 9.0 volts and less than 18 volts.
• Output speed exceeds 200 RPM.
• 4th range is selected and attained.
Conditions for Setting the DTC
DTC P0734 sets when the calculated 4th range ratio, steady
state, differs from the known 4th range ratio.
Action Taken When the DTC Sets
• The TCM illuminates the malfunction indicator lamp
(MIL).
• The transmission defaults to 5th 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 REVERSE, unless the
transmission is compromised by a direction change, then
the transmission will shift to NEUTRAL.
• If the shift selector is returned to a forward range and
the transmission is compromised by overspeeding or
direction change, the transmission will lock in NEUTRAL.
• DTC P0734 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
• Incorrect ratio codes typically indicate mechanical
conditions with specifi c clutches, such as 1-2-3-4 clutch
and 4-5-6 clutch, for 4th range.
• Incorrect ratio code could indicate a hydraulically failed
solenoid. Observe DTC information for specifi c solenoid.
• Clutch test mode can be used to observe stall speed.
• You may have to drive the vehicle in order to experience
a condition.