Dtc P0877 - Workhorse ALLISON 1000MH Service Manual

WORKHORSE CUSTOM CHASSIS
Service Manual

DTC P0877

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
for reverse pressure. Fluid pressure is supplied to the
pressure switch 4 (PS4) when the manual selector valve
is in any position except REVERSE. When the manual
selector valve is moved to REVERSE, pressure to PS4
is cut off, causing the switch to close.
DTC P0877 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
• DTC P0877 Transmission Pressure Switch 4 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.
• The transmission fl uid temperature (TFT) is greater than
0°C (32°F).
• DTC P0708 and P0878 is not active.
Conditions for Setting the DTC
DTC P0877 sets when P (PARK), N (NEUTRAL), or a forward
range is selected and the PS4 state remains in the mechanically
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closed/electrically ON position for greater than 1.0 second.
Action Taken When the DTC Sets
• The transmission control module (TCM) illuminates
• The transmission will lock in NEUTRAL.
• DTC P0877 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
• When diagnosing for an intermittent short or open,
• You may have to drive the vehicle in order to experience
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Automatic Transmission – Allison
the malfunction indicator lamp (MIL) during the second
consecutive trip in which the Conditions for Setting the
DTC are met.
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
massage the wiring harness while watching the test
equipment for a change.
2007 W Series Chassis
2007 W Series