HEAD ASSEMBLY PARTS SERVICE 6N9978 - Caterpillar

Pressure Sensors
Main Hydraulic Valve Supply Pressure Sensor
Illustration 3 g02571841The main hydraulic valve supply pressure sensor sends a PWM signal to the Implement ECM indicating system pressure. The duty cycle of the signal will vary in proportion to the system pressure. These PWM signals are inputs to the Implement ECM.Position Sensors
Lift/Tilt Lever Position Sensor
Illustration 4 g03371619The joystick lift position sensor sends a Pulse Width Modulated (PWM) signal to the Implement ECM indicating the position of the lift control lever. The position sensor is located in the base of the joystick. When the operator moves the joystick, the Implement ECM analyzes the signal from the joystick position sensor. The Implement ECM uses the sensor information, along with other conditions, to control the implement valve solenoids.Switches
Implement Lockout Switch
Illustration 5 g03015758The Implement ECM controls the operation of the Implement Pilot Supply Solenoid according to the position of the Hydraulic Lockout Switch. Certain fault conditions will also cause the Implement ECM to use the solenoid valve to disable hydraulic operation. When the switch is in the UNLOCK position, the normally closed switch contacts will ground the input circuit at ECM contact J1-34 and J1-33 is opened. When the ECM detects this grounded circuit, the ECM will energize the implement pilot supply solenoid. The energized solenoid allows pilot oil to be supplied to the implement control valve.When the switch is in the LOCK position, the normally open switch contacts will ground the input circuit at ECM contact J1-33 and J1-34 is opened. When the ECM detects this grounded circuit, the ECM de-energizes the ON/OFF output for the Implement Pilot Supply Solenoid. Pilot oil is blocked from the implement control valve.Fan Return Filter Bypass Switch
Illustration 6 g03015918The bypass switch is a pressure switch that shows whether the filter is plugged and the filter is being bypassed. The fan return filter bypass switch is a normally closed switch. The bypass switch will close at 500 kPa (73 psi) differential pressure notifying the ECM that the filter is plugged. The hydraulic filter bypass switch provides a ground to the ECM when activated.This switch is one of the inputs that is used in order to drive the "system indicator" in the instrument cluster. This indicator is turned ON when the switch is in the closed position and the oil temperature is greater than 52°