WORKHORSE CUSTOM CHASSIS
Service Manual
Automatic Transmission – Allison
2007 W Series
© 2006 Workhorse Custom Chassis — All Rights Reserved
SECTION
7.2
PAGE
63
2007 W Series Chassis
WSM082106
Pressure Switch Manifold
The PSM is a multiple-switch assembly made up of 3
N/O pressure switches, PS1 (4), PS2 (3), and PS3 (2)
and 1 N/C pressure switch. N/O pressure switches, PS1,
PS2, and PS3, correspond to shift valves SS1, SS2,
and SS3. Fluid pressures are fed from shift valves SS1,
SS2, and SS3 to the manual selector valve and to the
pressure switches based on the positions of the valves
and shift selector. The shift valve fl uid pressures refl ect
the logic condition at the corresponding solenoids. This
logic indicates the current transmission operating range
to the TCM.
The 3 fl uid pressure switches corresponding to the
shift valves are N/O, contacts not touching, when no
fl uid pressure is present, so that electrical current is
stopped at the switch. When fl uid pressure is routed to
the switch, it moves the diaphragm and upper contact
so that the contact element touches both the positive
and ground contacts. This closes the circuit and allows
current to fl ow from the positive contact and through the
switch.
Pressure switch 4 (PS4) (1) corresponding to REVERSE
is N/C, since fl uid pressure is always present unless the
selector valve is moved to REVERSE. The PSM also
contains a transmission fl uid temperature (TFT) sensor
thermistor (5) for sump temperature. Changes in sump
fl uid temperature are indicated by changes in sensor
resistance. Increasing temperature causes decreased
sensor resistance. The resistance value is then relayed
to the TCM as an input for shift control.
Internal Wiring Harness
The internal wiring harness has connectors for shift
solenoids SS1 (7), SS2 (3) and SS3 (4), PCS1 (6) and
PCS2 (5), TCC pressure control solenoid (TCC PCS)
(2), and the PSM (1). There is also a connector for the
modulated main (MOD MAIN) pressure solenoid (9)
and the IMS (10). All of these connectors go to the main
