SPRING AS-GAS 3574260 - Caterpillar

The transmission modulating solenoid valves that are located on the transmission, direct pilot oil to the ends of the control spool. The control spool will shift allowing pressure oil to the corresponding clutches. The power train ECM activates the transmission modulating valves. The ECM receives input from the following switches: direction switch, upshift switch and downshift switch. In order for the machine to move, two transmission solenoid valves must be activated. When the transmission is in neutral, no solenoid valves are activated.Neutral Start Operation
The neutral start feature requires the direction switch to be in the NEUTRAL position, before the engine will crank. The operator controls this feature by placing the direction switch in the neutral position and turning the key start switch to the START position. This feature allows the engine to start only when the transmission is in the NEUTRAL position. When this feature is in operation, the power train ECM activates the start relay. The start relay allows the starting motor to turn.Parking Brake Operation
The parking brake function prevents the operator from operating the machine while the parking brake is engaged. Driving through the parking brake causes accelerated wear to the friction components of the parking brake.When the parking brake control is disengaged, the transmission will shift normally. When the parking brake control is engaged, the transmission will not shift out of neutral to first speed forward or first speed reverse. If the transmission is in first speed forward or in first speed reverse and the parking brake is moved to the engaged position, the transmission will shift into neutral. All of the clutch solenoid modulating valves are de-energized. If the transmission is in second speed forward or in third speed forward, the transmission will remain engaged.The parking brake function activates a warning category 1 or a warning category 3 on the Caterpillar Monitoring System.Warning category 1 is activated whenever the parking brake is engaged. The parking brake indicator will flash.While the parking brake is engaged, warning category 3 will be activated. This will occur if the operator places the transmission direction control switch in the FORWARD position or the REVERSE position. The parking brake indicator will flash and the action lamp will flash. The action alarm will sound.When the parking brake is engaged and the transmission is in first speed, the power train ECM shifts the transmission to neutral. The power train ECM also sends the parking brake status to the Caterpillar Monitoring System via the CAT Data Link. When the parking brake is engaged, the alert indicator for the parking brake flashes on the Caterpillar Monitoring System. If the operator selects the FORWARD position or the REVERSE position and the parking brake is engaged, the Caterpillar Monitoring System initiates a Warning Category 3. A Warning Category 3 causes the parking brake indicator and the action lamp to flash. The action alarm will also sound.Reference: For more information on the Caterpillar Monitoring System, refer to the Service Manual module Systems Operation, "Caterpillar Monitoring System" for