DISC 8U2545 - Caterpillar

Propulsion Override System
Illustration 2 g01427755
Propulsion Override Circuit (1) B+ from main relay (2) Limp home circuit breaker (3) Propulsion resistor "1" (4) Propulsion resistor "2" (5) Parking brake solenoid (6) Left propulsion override switch (7) Right propulsion override switch (8) To left operator control unit terminal "J2-6" (9) To machine ECM terminal "J1-50" (10) Left propulsion forward solenoid (11) Left propulsion reverse solenoid (12) Right propulsion forward solenoid (13) Right propulsion reverse solenoidIf the machine electronic control system detects a fault which prevents the machine from moving, or if a computer module is faulty, the propulsion override switches can be used to bypass the electronic controls so that the machine can be moved. The left and right tracks can be controlled independently. Power is transferred through the 122-BU wire from the limp home circuit breaker to contact "5" of the left and right propulsion override switches. The 122-BU wire also transfers power to two resistors. On the downstream side of the resistors, reduced power is available to contact "2" of the left propulsion override switch through the A340-YL wire. Reduced power is also available to contact "2" of the right propulsion override switch through the A327-WH wire.Note: The resistors in the circuits to contact "2" of the propulsion override switches limit the speed the machine will travel when the propulsion override switches are used. When the left propulsion override switch is in the REVERSE position, power transfers across contact "1" and contact "2" of the switch and to the left reverse EDC. Power also transfers across contact "4" and contact "5" of the left switch to the parking brake solenoid. The left reverse EDC and the parking brake solenoid energize, and the left track moves in reverse.When the right propulsion override switch is in the REVERSE position, contact "1" and contact "2" of the switch are closed, and contact "4" and contact "5" of the switch are closed. Power transfers to the right reverse EDC, and power transfers to the parking brake solenoid. The right track then moves in reverse.When the propulsion override switches are in the FORWARD position, the forward EDCs are energized and the parking brake solenoid is energized. In this case, the machine moves forward. If one of the override switches is in the FORWARD position and the other switch is in the REVERSE position, the tracks will counterrotate.