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WORKHORSE CUSTOM CHASSIS
Service Manual
2007 W Series
SECTION
7.2
PAGE
272
Automatic Transmission – Allison
2007 W Series Chassis
© 2006 Workhorse Custom Chassis — All Rights Reserved
WSM082106
DTC P0842
Circuit Description
The pressure switch manifold (PSM) is a multiple-
switch assembly made up of 3 normally open (N/O)
pressure switches and 1 normally closed (N/C) pressure
switch. Pressure switch 1 (PS1) monitors shift valve
1 positioning and relays it to the transmission control
module (TCM).
DTC P0842 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
• DTC P0842 Transmission Pressure Switch 1 Circuit Low
Conditions for Running the DTC
• 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.
• Shift valve 1 is commanded to the OFF, destroked,
position.
Conditions for Setting the DTC
DTC P0842 sets during steady state operation when PS1
indicates ON for 125 milliseconds after shift solenoid 1 (SS1) has
been commanded OFF.
Action Taken When the DTC Sets
• The TCM illuminates the malfunction indicator lamp
(MIL).
• When in a forward range, the transmission will fail
to another forward range, unless the transmission is
compromised by overspeeding or direction change, then
the transmission will shift to NEUTRAL while diagnostic
response is active.
• If the shift selector is moved from a forward range to
NEUTRAL or from a forward range to REVERSE, then
the transmission will shift to NEUTRAL.
• If the shift selector is moved to REVERSE, the
transmission will shift to REVERSE if it is not
compromised by overspeeding or a direction change. If
compromised, the transmission will shift to NEUTRAL.
• DTC P0842 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
– A damaged terminal
– Poor terminal tension
– A chafed wire
– A broken wire inside the insulation