The Power Train/Chassis Electronic Control Module (Power Train/Chassis ECM) receives input signals from pressure switches in the braking system. If a braking system failure occurs and accumulator oil pressure is lost, the Power Train/Chassis ECM will automatically engage the parking brake.
If the machine is equipped with the optional transmission oil pressure sensor, the Power Train/Chassis ECM also receives an input signal from this sensor. If transmission oil pressure is lost, the Power Train/Chassis ECM will automatically engage the parking brake. This may be caused by a transmission hydraulic failure, a stalled engine, or other failure.
Reference: For further information on the automatic parking brake function, refer to Power Train Electronic Control System, Systems Operation, Troubleshooting, Testing and Adjusting, "Automatic Brake Function" for the machine that is being serviced.
Brake Accumulator Oil Pressure Switches
 | |
| Illustration 1 | g00993365 |
Location of the brake accumulator oil pressure switches (1) Brake accumulator oil pressure switch - alert indicator (2) Brake accumulator oil pressure switch - brake application | |
The brake accumulator oil pressure switches are located on the accumulator charging valve. The accumulator charging valve is located on the left side of the front frame, in the transmission compartment.
When the machine is started, brake accumulator oil pressure increases. When the pressure reaches 8275 kPa (1200 psi) pressure switch (2) closes. The Power Train/Chassis ECM receives this signal and will allow the parking brake to be disengaged.
 | |
| Illustration 2 | g00881163 |
AVSpare Monitoring System display (1) Brake accumulator oil pressure alert indicator | |
When the pressure increases to 9500 kPa (1380 psi) pressure switch (1) closes. The Power Train/Chassis ECM receives a signal from the oil pressure switch. The Power Train/Chassis ECM then sends a signal to the AVSpare Monitoring System over the AVS Data Link. The AVSpare Monitoring System will then turn off brake accumulator oil pressure alert indicator (3) on the AVSpare Monitoring System display.
If brake accumulator oil pressure decreases to 8275 ± 345 kPa (1200 ± 50 psi) pressure switch (1) will open. The Power Train/Chassis ECM receives this signal and sends it to the AVSpare Monitoring System. The AVSpare Monitoring System will activate alert indicator (3) .
If machine operation is continued and brake accumulator oil pressure decreases to 6890 ± 345 kPa (1000 ± 50 psi), pressure switch (2) will open. The Power Train/Chassis ECM receives this signal and automatically engages the parking brake.
Once the parking brake has been engaged, the parking brake will remain engaged until the brake accumulator oil pressure rises above 8270 kPa (1200 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 further 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.
Transmission Oil Pressure Sensor (If Equipped)
 | |
| Illustration 3 | g01006911 |
Location of the transmission oil pressure sensor (4) Transmission oil pressure sensor | |
Transmission oil pressure sensor (4) is located on the right side of the transmission. 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.
 | |
| Illustration 4 | g00881165 |
AVSpare 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 AVS data link to the AVSpare Monitoring System. The AVSpare Monitoring System will then activate transmission oil pressure alert indicator (5) on the AVSpare 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 1515 kPa (220 psi), the Power Train/Chassis ECM will automatically 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.
Reference: For further 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.