Dtc P0842 - Workhorse ALLISON 1000MH Service Manual

WORKHORSE CUSTOM CHASSIS
Service Manual

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).
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• When in a forward range, the transmission will fail
• If the shift selector is moved from a forward range to
• If the shift selector is moved to REVERSE, the
• DTC P0842 is stored in TCM history.
• The TCM freezes shift adapts.
• The TCM inhibits torque converter clutch (TCC)
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
© 2006 Workhorse Custom Chassis — All Rights Reserved
Automatic Transmission – Allison
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.
NEUTRAL or from a forward range to REVERSE, then
the transmission will shift to NEUTRAL.
transmission will shift to REVERSE if it is not
compromised by overspeeding or a direction change. If
compromised, the transmission will shift to NEUTRAL.
engagement.
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
2007 W Series Chassis
2007 W Series