WIRE AS 1709478 - Caterpillar

Illustration 1 g00518513
(1) Secondary brake and parking brake pressure switch Some input signals to the Power Train Electronic Control Module (Power Train ECM) during a shift can cause a hunting condition of the transmission. A hunting condition is a series of rapid, unwanted transmission upshifts and rapid, unwanted transmission downshifts. A hunting condition is caused by ground speed changes near a transmission shift point.The Power Train ECM is designed to prevent a hunting condition. After two seconds, the Power Train ECM will allow one shift back to the original gear.In normal operating conditions, a rapid shift may be necessary. An example of a normal operating condition is stopping the machine. If a rapid downshift is not made in this example, the engine will stop. When the secondary brake or the parking brake is used, the secondary brake and parking brake pressure switch (1) will signal the Power Train ECM that rapid shifts are necessary.When the secondary brake and parking brake pressure switch (1) is open, the ground to the Power Train ECM is removed. The Power Train ECM will then determine that a rapid shift is necessary. Whenever the secondary brakes or the parking brakes are engaged, the Power Train ECM will shift rapidly.When the secondary brake and parking brake pressure switch (1) is closed, a ground to the Power Train ECM is created. The Power Train ECM then allows one shift back to the previous gear.