HEAD 4Z6171 - Caterpillar

Illustration 1 g01354776
Illustration 2 g02459189
Schematic of the Parking Brake Function circuit connections.The Parking Brake on the machine is ENGAGED with the use of a spring force that locks the transmission in place to prevent movement. When one of the Transmission Gear Shift solenoids is energized, the hydraulic force counters the force of the springs to DISENGAGE the parking brake. When the Machine ECM determines that the Parking Brake must be ENGAGED, the ECM will de-energize both of the transmission solenoids. De-energizing the solenoids allows the spring to ENGAGE the parking brake.The ECM sends a signal to the Soft Switch Panel (SSP) to illuminate the LED indicator above the Parking Brake Button.The ECM controls the Parking Brake under the following conditions.
When no machine travel is detected from the Transmission Output Speed Sensor (TOS) and the Parking Brake Button is pressed, the ECM will ENGAGE the Parking Brake.
When no machine travel is detected from the Transmission Output Speed (TOS) Sensor and the left armrest is moved to the RAISED position, the ECM engages the Parking Brake. The ECM will DISENGAGE the Parking Brake when the armrest is moved to the DOWN position if no ENGAGE command has been received from the SSP button.
If the Back Up Mode is active, the ECM will DISENGAGE the Parking Brake.
If the Parking Brake is ENGAGED and the Brake System Pressure Sensor indicates that the service brake pedal is depressed. The ECM will DISENGAGE the Parking Brake when the Brake System Pressure Sensor indicates that the service brake pedal is released.
When the Parking Brake is ENGAGED and the Parking Brake switch on the SSP is pressed, the ECM will energize the selected gear solenoid in order to DISENGAGE the Parking Brake.If there is an active diagnostic code for the Armrest Position Switch or the Brake System Pressure Sensor, the Parking Brake will be ENGAGED unless the service brake is locked or the machine is traveling as indicated to the ECM by the TOS sensor.