The Power Train ECM also receives an input signal from the transmission oil pressure sensor for the electronic transmission control. If transmission oil pressure is lost, the Power Train ECM will automatically engage the parking brake. This may be caused by a transmission hydraulic failure, a stalled engine, or other failure.
Reference: For information on the automatic parking brake function, refer to Power Train Electronic Control System, Systems Operation, Troubleshooting, Testing and Adjusting, "Power Train Electronic Control System" for the machine that is being serviced.
Low Service Brake Oil Pressure
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| Illustration 1 | g01032562 |
Left side view of the rear frame (1) Brake accumulator oil pressure switch for the alert indicator (2) Brake accumulator oil pressure switch for brake application | |
When the engine is started, brake accumulator oil pressure increases. When the pressure reaches 5857 ± 345 kPa (850 ± 50 psi) pressure switch (2) closes. The Power Train ECM receives this signal and will allow the parking brake to be disengaged.
When the pressure increases to 10700 kPa (1550 psi) pressure switch (1) closes. The Caterpillar Monitoring System receives a signal from the oil pressure switch. The Caterpillar Monitoring System will then turn off the brake accumulator oil pressure alert indicator on the Caterpillar Monitoring System display.
If the brake accumulator hydraulic oil pressure decreases to 9000 ± 540 kPa (1300 ± 78 psi), pressure switch (1) will open and the brake accumulator oil pressure alert indicator on the Caterpillar Monitoring System display will come on. This will warn the operator of low brake accumulator hydraulic oil pressure. If machine operation is continued and the brake accumulator hydraulic oil pressure decreases to 5168 ± 172 kPa (750 ± 25 psi), pressure switch (2) will open. Pressure switch (2) sends a signal to the Power Train ECM and the parking brake will automatically engage.
Once the parking brake has been engaged, the parking brake will remain engaged until the brake accumulator oil pressure increases above 5857 ± 345 kPa (850 ± 50 psi). The operator must then cycle the parking brake switch from the ON position to the OFF position in order to disengage the parking brake.
Reference: For information on the brake accumulator oil pressure switches, refer to Power Train Electronic Control System, Systems Operation, Troubleshooting, Testing and Adjusting, "Switches" for the machine that is being serviced.
Low Transmission Oil Pressure
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| Illustration 2 | g01035022 |
Rear view of the transmission (3) Transmission oil pressure sensor for alert indicator and brake application | |
The oil pressure sensor senses the oil pressure in the transmission hydraulic system. The oil pressure sensor sends a signal to the Power Train ECM.
During normal machine operation, the transmission oil pressure will be 2550 ± 70 kPa (370 ± 10 psi). The Power Train ECM will sense this pressure through oil pressure sensor (3). If the transmission oil pressure decreases to 550 kPa (80 psi), the Power Train ECM will send a signal over the CAT Data Link to the Caterpillar Monitoring System. The Caterpillar Monitoring System will then activate the transmission oil pressure alert indicator on the Caterpillar Monitoring System display. The alert indicator will remain activated until the pressure increases above 550 kPa (80 psi).
If machine operation is continued and transmission oil pressure decreases below 450 kPa (65 psi), the Power Train ECM will automatically engage the parking brake.
The parking brake will remain engaged until the transmission oil pressure increases above 550 kPa (80 psi). The operator must then cycle the parking brake switch from the ON position to the OFF position in order to disengage the parking brake.
Reference: For information on the transmission oil pressure sensor, refer to Power Train Electronic Control System, Systems Operation, Troubleshooting, Testing and Adjusting, "Sensors" for the machine that is being serviced.