The Power Train/Chassis ECM also receives an input signal from a transmission oil pressure sensor. If transmission oil pressure is lost, the Power Train/Chassis ECM will automatically engage the parking brake. A transmission hydraulic failure, a stalled engine, or other failure will cause the parking brake to engage automatically.
Low Service Brake Oil Pressure
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| Illustration 1 | g03675320 |
Location of the brake accumulator oil pressure sensor (1) Brake accumulator oil pressure sensor (2) Brake accumulator charging valve | |
When the engine is started, brake accumulator oil pressure increases. When the oil pressure reaches the actuation pressure for pressure sensor (1), the sensor will send a signal to the Power Train/Chassis ECM. The Power Train/Chassis ECM receives this signal and will allow the parking brake to be disengaged.
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| Illustration 2 | g03693721 |
Caterpillar Monitoring System display (3) Brake accumulator oil pressure alert indicator | |
When the oil pressure increases to the actuation pressure for pressure sensor (1), the pressure sensor will send a signal to the Power Train/Chassis ECM. The Power Train/Chassis ECM receives a signal from the oil pressure sensor. The Power Train/Chassis ECM then sends a signal to the Caterpillar Monitoring System over the CAT Data Link. The Caterpillar Monitoring System will then turn off brake accumulator oil pressure alert indicator (3) on the Caterpillar Monitoring System display.
If brake accumulator oil pressure decreases to the deactuation pressure for pressure sensor (1), the sensor will open. The Power Train/Chassis ECM receives this signal and sends to the Caterpillar Monitoring System. The Caterpillar Monitoring System will activate alert indicator (3) .
If machine operation is continued and brake accumulator oil pressure further decreases, pressure sensor (1) will signal the Power Train/Chassis ECM. The Power Train/Chassis ECM receives this signal and engages the parking brake.
The parking brake will remain engaged until the brake accumulator oil pressure rises above the actuation pressure for pressure sensor (1). The operator must then cycle the parking brake sensor from the ON position to the OFF position in order to disengage the parking brake.
ReferenceFor further information on the brake accumulator oil pressure sensors, refer to Power Train Electronic Control System, Systems Operation, Troubleshooting, Testing and Adjusting, "Sensors".
Low Transmission Oil Pressure
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| Illustration 3 | g01157117 |
(4) Transmission oil pressure sensor | |
Transmission oil pressure sensor (4) is located on the left side of the transmission compartment. The oil pressure sensor senses the oil pressure in the transmission hydraulic system. The oil pressure sensor sends a signal to the Power Train/Chassis ECM.
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| Illustration 4 | g03693722 |
Caterpillar Monitoring System display (5) Transmission oil pressure alert indicator | |
During normal machine operation, the transmission oil pressure will be 2690 to 3205 kPa (390 to 465 psi). The Power Train/Chassis ECM will sense this pressure through oil pressure sensor (4). If the transmission oil pressure decreases to 1725 kPa (250 psi), the Power Train/Chassis ECM will send a signal over the CAT data link to the Caterpillar Monitoring System. The Caterpillar Monitoring System will then activate transmission oil pressure alert indicator (5) on the Caterpillar Monitoring System display. The alert indicator will remain activated until the pressure rises above 1725 kPa (250 psi).
If machine operation is continued and transmission oil pressure decreases below 1585 kPa (230 psi), the Power Train/Chassis ECM will engage the parking brake.
Once the parking brake has been engaged, the parking brake will remain engaged until the transmission oil pressure increases above 1725 kPa (250 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.
Note: If a loss of transmission oil pressure occurs and the machine is to be towed, reconfiguring the transmission oil pressure sensor as "Not Installed" is required. The transmission oil pressure sensor can be configured in the Caterpillar Electronic Technician (ET) as "Installed" or "Not Installed". Also the sensor can be temporarily overridden in the Caterpillar Monitoring System submode 7.7.
ReferenceFor further information on the transmission oil pressure sensor, refer to Power Train Electronic Control System, Systems Operation, Troubleshooting, Testing and Adjusting, "Sensors".