TM 5-3805-291-23-1
THEORY OF OPERATION - CONTINUED
0003 00
POWERTRAIN - CONTINUED
(3)
Pressure Switch (Parking Brake).
(a) Parking brake pressure switch is an input of powertrain ECM which informs powertrain ECM when
parking brake is engaged.
N OT E
The normally closed (N/C) circuit and normally open (N/O) circuit of the parking brake pressure switch are
used for diagnostic purposes. A circuit failure is present if the two circuits are open at the same time or if
the two circuits are grounded at the same time. This fault is then shown on the powertrain ECM display.
(b) Parking brake pressure switch is a double-pole, single-throw pressure switch. When an operator disen-
gages parking brake, normally open (N/O) pole opens and normally closed (N/C) pole closes to
ground. This tells powertrain ECM that parking brake is disengaged. When parking brake is engaged,
N/O pole is closed and N/C pole is open. This tells powertrain ECM that parking brake pressure
switch circuit is operating correctly and parking brake is engaged. No action is required.
(c) N/C pole connects to powertrain ECM connector contact J2-53. N/O pole connects to powertrain
ECM connector contact J2-52. Switch common terminal connects to ground.
(4)
Pressure Switch (Primary Steering).
(a) Primary steering pressure switch is an input of powertrain ECM which informs powertrain ECM of
primary steering system status.
(b) Primary steering pressure switch is a double-pole, single-throw pressure switch. When primary steer-
ing pressure drops below threshold pressure of 102 15 psi (700 100 kPa), primary steering pres-
sure switch will change. Powertrain ECM will activate primary steering warning indicator and engage
secondary steering system. When primary steering system functions correctly, N/O pole is closed and
N/C pole is open. No action is required.
N OT E
The normally closed (N/C) circuit and normally open (N/O) circuit of the primary steering pressure switch
are used for diagnostic purposes. A circuit failure is present if the two circuits are open at the same time or
if the two circuits are grounded at the same time. This fault is then shown on the powertrain ECM display.
(c) N/C pole connects to powertrain ECM connector contact J2-38. N/O pole connects to powertrain
ECM connector contact J2-37. Switch common terminal connects to ground.
0003 00-36
