12M Series 3, 140M Series 3, 160M Series 3, 140, 150 and and 160 Motor Graders Hydraulic System Caterpillar


Hydraulic System
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1.1. Joystick Operation
2.2. Operation of the Joystick Position Sensor
3.2. Operation of the Left-hand Joystick
4.3. Blade Lift, Articulation, Wheel Lean Position Sensors
5.3. Joystick Switches
6.2. Operation of the Right-hand Joystick
7.3. Position Sensors
8.2. Advanced Control Joystick
9.1. Auxiliary Hydraulics
10.2. Auxiliary Hydraulic Control Operation
11.3. Advanced Control Joystick (ACJ) Position Sensors
12.2. Hydraulic Float Function
13.2. Configuring Auxiliary Hydraulic Control

The hydraulic system is composed of the following components:

  • Implement and steering pump

  • Pilot control manifold

  • Steering control valve

  • Implement control valves

  • Cylinders and the circle drive

  • Shutoff valve

The piston pump transfers oil from the tank to the pilot control manifold. The pilot control manifold will send some of the pump supply oil to the shutoff valve and then to the pilot system. The oil that is not used by the pilot system will flow to the steering control valve. The steering system has priority over the implement system. When the demands of the steering circuit are met, the steering control valve will direct oil to the implement circuit. Oil flows from the steering control valve to the implement control valves. The implement control valves will direct oil to the cylinders or circle drive.



Illustration 1g03523156
(1) Articulation Cylinders
(2) Left-Hand Blade Cushion Accumulator and Solenoid Valve
(3) Left-hand Blade Lift Cylinder
(4) Right-hand Blade Cushion Accumulator and Solenoid Valve
(5) Right-hand Blade Lift Cylinder
(6) Signal Relief Valve
(7) Right-hand Blade Lift Control Valve
(8) Left-hand Blade Lift Control Valve
(9) Articulation Control Valve
(10) Implement ECM 2
(11) Left-hand Joystick Connector 1
(12) Left-hand Joystick Connector 2
(13) Implement ECM 1
(14) Right-hand Joystick Connector 1


Illustration 2g03525321
(15) Wheel Lean Cylinder
(16) Circle Drive Motor
(17) Centershift Cylinder
(18) Side Shift Cylinder
(19) Blade Tip Cylinder
(20) Blade Tip Control Valve
(21) Swivel
(22) Side Shift Control Valve
(23) Centershift Control Valve
(24) Circle Drive Control Valve
(25) Wheel Lean Control Valve
(26) Implement ECM 1
(27) Left-hand Joystick Connector 2
(28) Implement ECM 2
(29) Right-hand Joystick Connector 1

There are eight standard implement circuits on the machine. Seven control valves are for cylinder circuits and one control valve is for the motor that rotates the blade around the drawbar. The hydraulic system can accommodate as many as 14 implement control valves. The individual control valves regulate the operation of each implement. When the operator moves the joystick control, an electrical signal is sent to a directional solenoid. When the solenoid is energized, pilot oil will be directed to one side of the valve spool. The valve spool will shift. Oil will be directed to the corresponding implement.

Some of the Motor Graders may have different implements. The number of the control valves in each valve group may vary. When an implement control valve is replaced, use the same part number. Using the same part number will keep the control valve and the cylinder matched.

Reference: For additional information on the hydraulic system, refer to the hydraulic schematic for your machine.

Joystick Operation



Illustration 3g03735327
Functions of the left and right joysticks that are controlled by the modules of the Implement ECM (Shown with Optional "Advanced Control Joysticks")
(1) Downshift switch
(2) Wheel lean control (left)
(3) Upshift switch
(4) Wheel lean control (right)
(5) Automatic articulation centering control
(6) Steer left
(7) Steer right
(8) Blade lower and blade float for left side
(9) Blade lift for left side
(10) Articulation control
(11) Blade sideshift control (left)
(12) Blade sideshift control (right)
(13) Blade lower and blade float for right side
(14) Blade lift for the right side
(15) Centershift control (left)
(16) Centershift control (right)
(17) Blade pitch control (forward)
(18) Blade pitch control (backward)
(19) Blade circle drive control
(20) Grade Control Auto/Manual switch (Left Side)
(21) Grade Control Side Shift Auto/Manual switch
(22) Grade Control Increment/Decrement switch (Left Side)
(23) Grade Control Increment/Decrement switch (Right Side)
(24) Grade Control Auto/Manual switch (Right Side)
(25) Not Used

Note: The illustration above shows the functions that are controlled by the Implement ECM's. The functions that are controlled by the Transmission/Chassis ECM are not called out in this manual. Refer to the manual for the Transmission/Chassis ECM for the joystick functions that are controlled by the Transmission/Chassis ECM.

The Implement ECM on the M Series 3 Motor Graders enables the operator to use the electronic left and right joysticks. The joysticks control movement of an implement or function. The joysticks are equipped with position sensors and switch-to-ground type switches that send input signals to the ECM.

Operation of the Joystick Position Sensor

Any movement of the joystick handle on a specific axis is detected by an internal position sensor for that axis. When the position sensor is powered up, the sensor will continuously send a Pulse Width Modulated (PWM) signal to the ECM. The duty cycle of the PWM signal from the sensor will change in response to the direction and the amount of movement of the joystick. The duty cycle is the comparison between the percentage of time that the signal is high and time the signal is low for one cycle. The ECM will recognize a valid duty cycle that ranges from 10 ± 5 percent to 90 ± 5 percent. A joystick that is in the center or the neutral position would result in a duty cycle signal of approximately 50 ± 6 percent.

The amount of current applied to a proportional solenoid determines the amount of pilot oil pressure that is applied to a control valve. An increase in the amount of electrical current that is applied to the solenoid will increase the movement of a valve spool. The increase of current will result in an increase of hydraulic flow to a cylinder.

When movement of more than one joystick axis is detected, the ECM will send output current signals to multiple solenoids or controls. These signals will move the implement in several directions at the same time.

Operation of the Left-hand Joystick

All of the internal components and the harness circuits have assigned diagnostic codes. The Implement ECM, or Implement ECM 2, activate a diagnostic code for a component when abnormal conditions are detected in the involved circuit.

Two ground sources are connected to all of the internal components of the joystick. Both of the ground circuits must fail, internally or externally, in order for the component not to function due to loss of ground connections.

Blade Lift, Articulation, Wheel Lean Position Sensors

The blade left lift position sensor, the machine articulation position sensor and the wheel lean position sensor are located in the left joystick. The axis assignments and details are listed below:

Blade Left Lift Position Sensor - Assigned to the forward/rearward axis. The position sensor outputs a PWM signal. The signal frequency of the sensor is approximately 500 ± 100 Hz. The position sensor sends a PWM input signal to the Implement ECM. The duty cycle of the signal will vary from full rearward to full forward positions of the joystick, 10 ± 5 to 90 ± 5 percent, respectively. When the lever is in the center position, the duty cycle will be approximately 50 ± 6 percent. When the joystick is moved to a full forward detent position, the ECM will enable the float mode for the left lift hydraulic valve.

Articulation Position Sensor - Assigned to the twist left/right axis. The position sensor outputs a PWM signal. The frequency of the sensor signal is approximately 500 ± 100 Hz. The position sensor sends a PWM input signal to the Implement ECM 2. The duty cycle of the signal will vary from the full rotate left position to the full rotate right position, 10 ± 5 to 90 ± 5 percent, respectively. When the joystick is in the center (neutral) position, the duty cycle will be approximately 50 ± 7 percent.

Wheel Lean Position Sensor - Assigned to the left/right rocker button axis on the joystick handle. The position sensor outputs a PWM signal. The frequency of the sensor signal is approximately 500 ± 100 Hz. The position sensor sends a PWM input signal to the Implement ECM. The duty cycle of the signal will be approximately 10 ± 5 percent when the joystick left button for the wheel lean is fully depressed. The duty cycle of the signal will be approximately 90 ± 5 percent when the joystick right button for the wheel lean is fully depressed. When neither button is depressed, the duty cycle will be approximately 50 ± 7 percent.

Joystick Switches

The neutral articulation switch is the only switch on the left joystick that provides inputs to the Implement ECM. The switch provides two ground types of input to the ECM. The switch is connected to two of the four return circuits of the sensor. The switch must lose both of the ground circuits in order to cause a circuit failure.

Since there is ECM pull-up voltage present at the contacts of the switch input, the switch contact that is not grounded will be pulled high. The ECM expects to detect one switch circuit that is grounded and one switch circuit that is high at all times. If both of the circuits are high or grounded at the same time, the ECM will activate a diagnostic code for the switch.

Operation of the Right-hand Joystick

The right-hand joystick receives power connections and ground connections from two separate 10 V sensor power supply circuits. One power supply from the Implement ECM and one power supply from the Transmission/Chassis ECM. As shown in the illustration above, each position sensor is internally connected to both of the power supply circuits. The position sensors are inside of the joystick. Each switch is connected to both of the return circuits of the sensor that are inside of the joystick.

All of the internal components and the harness circuits that are controlled by the Implement ECM have diagnostic codes that are assigned. The ECM will activate the diagnostic code for a component when an abnormal condition is detected in the involved circuit.

When two power and ground sources connect to a component, both power circuits must fail, or both ground circuits must fail. These events must occur, in order for the component to fail to function correctly.

Position Sensors

The position sensors that are located on the inside of the assembly of the right joystick send a PWM signal to the Implement ECM. Each of the position sensors will output a PWM signal at a frequency of approximately 500 ± 100 Hz to the Implement ECM. The assignments for the axis and the details are listed below:

Blade Right Lift Position Sensor - Assigned to the forward/rearward axis. The duty cycle will vary from full rearward to the full forward position of the lever at 10 ± 5 percent to 90 ± 5 percent, respectively. When the lever is in the center position, the duty cycle will be approximately 50 ± 6 percent. When the joystick is moved to a full forward detent position, the ECM will enable the float mode for the right lift hydraulic valve.

Blade Side Shift Position Sensor - Assigned to the left/right axis. The sensor signal duty cycle will be approximately 10% (± 5) when the joystick is at the full left position. The duty cycle will be approximately 90% (± 5) when the joystick is at the full right position. When the joystick is in the center position, the duty cycle will be approximately 50 ± 7 percent.

Blade Circle Drive Position Sensor - Assigned to the twist left/right axis. The sensor signal duty cycle will be approximately 10% (± 5) when the joystick is rotated to the full left position. The duty cycle will be approximately 90% (± 5) when the joystick is rotated to the full right position. When the joystick is in the center position, the duty cycle will be approximately 50% (± 5).

Blade Center Shift Position Sensor - Assigned to the left/right axis on the "thumbrocker" switch on the handle of the joystick. The sensor signal duty cycle will be approximately 10% (± 5) when the "thumbrocker" switch is at the full left position. The duty cycle will be approximately 90% (± 5) when the "thumbrocker" switch is at the full right position. When the "thumbrocker" switch is in the center position, the duty cycle will be approximately 50% (± 5).

Blade Pitch Position Sensor - Assigned to the forward/rearward axis on the "thumbrocker" switch on the handle of the joystick. The sensor signal duty cycle will be approximately 10% (± 5) when the "thumbrocker" switch is at the full lower position. The duty cycle will be approximately 90% (± 5) when the "thumbrocker" switch is at the full upper position. When the "thumbrocker" switch is in the center position, the duty cycle will be approximately 50% (± 5).

Advanced Control Joystick

Advanced Control Joystick (ACJ) can be used with Grade Control or Auxiliary Hydraulics. ACJ's are standard on machines with Grade Control and optional with Auxiliary Hydraulics.

Auxiliary Hydraulics



Illustration 4g01372895
"Auxiliary Control Pod" with Mini Joystick with control levers 1, 2, 3, 4, 5, and 6


Illustration 5g01316090
"Auxiliary Levers No. 6 and No. 7"


Illustration 6g03736142
"Advanced Control Joysticks" with "Auxiliary Levers No. 8 and No. 9"
(1) Left-hand Lever No. 8 Thumbwheel
(2) Right-hand Lever No. 9 Thumbwheel
(3) Not Used
(4) Float LED Indicator
(5) Not Used
(6) Float ON/OFF Switch
(7) Cat Grade Control Favorites

Note: The illustrations show all possible components that can be installed in the auxiliary hydraulic system. The components that are installed on your machine are dependent on the machine configuration.

The Implement ECM modules control the attachment auxiliary hydraulic system. Different combinations of auxiliary control levers that control the hydraulic valves can be installed on the machine. A full complement of auxiliary control levers and valves will allow six separate auxiliary hydraulic circuits to be available for the control of implement attachments. The Implement ECM can be configured to allow any one auxiliary control lever to control any one of the auxiliary hydraulic valves on the machine.

Auxiliary Hydraulic Valve 7 is not available on M3 Motor Graders.

The Implement ECM can be configured using Cat ET. Configuring the auxiliary hydraulic system enables assignment of any one auxiliary control lever to control any one of the hydraulic valves on the machine. Refer to "Configuring Auxiliary Hydraulic Control".

The configuration of the auxiliary hydraulic system will determine if the "Implement ECM 3" is installed. The solenoid outputs for two auxiliary hydraulic valves are controlled by the "Implement ECM 2". "Implement ECM 3" controls the solenoid outputs for the other four possible auxiliary hydraulic valves. If only two auxiliary hydraulic control levers for control of the two valves are installed on the machine, "Implement ECM 3" is not needed.

Depending on the auxiliary hydraulic configuration of your machine, some (not all) of the following components could be installed for control of the system:

  • The Implement ECM, "Implement ECM 2", "Implement ECM 3"

  • Auxiliary Control Pod (control lever no's. 1, 2, 3 and 4)

  • Stand alone auxiliary "thumbrocker" switch control lever no. 7

  • Stand-alone auxiliary "thumbrocker" control combination lever no. 7 and lever no. 6 (available only if no auxiliary control pod is installed)

  • Mini Joystick (only available with auxiliary control pod - adds lever no's. 5 and 6)

  • Two proportional solenoids and a valve for each auxiliary control lever installed

  • "Advanced Control Joystick" with lever no. 8 and lever no. 9 thumbwheel and float control switch

The different combinations of auxiliary hydraulic control levers that can be installed in the system are:

  • The stand-alone "thumbrocker" lever no. 7

  • The stand-alone "thumbrocker" levers no. 6 and no. 7

  • The auxiliary control pod (without the mini joystick)

  • The auxiliary control pod (without the mini joystick) and the stand-alone "thumbrocker" lever no. 7

  • "Advanced Control Joystick" with lever no. 8 and lever no. 9 thumbwheel and float control switch

Status all auxiliary hydraulic valves on the machine must be "installed" in the Cat ET configuration screen, before the ECM will enable operation. Also, the "Auxiliary Control Pod" enable status must be set to “enabled”.

Auxiliary Hydraulic Control Operation

Each control lever installed on the machine contains an internal position sensor. When powered up, that sensor sends a constant Pulse Width Modulated (PWM) signal to either the Implement ECM or the "Implement ECM 2". The ECM that the particular signal circuit is connected to depends on the control levers that are installed. Each installed lever position sensor circuit is monitored by the ECM for diagnostics. If the ECM detects a problem in the signal circuit, the ECM will activate a diagnostic code for the circuit.

The duty cycle of the control lever PWM sensor signal changes depending on the direction and the amount of lever movement. Duty cycle is the percentage of time a signal is high, compared to the percentage of time the signal is low, for one full cycle. The duty cycle signal from a typical position sensor the ECM will recognize as valid is from 10 (±5) percent to 90 (±5) percent. That range of Duty Cycle percentage is measured at the extreme ends of lever travel. A control lever that is in the center or the neutral position would result in a duty cycle signal of approximately 50 ± 5 percent.

The ECM uses the PWM duty cycle signals received from a control lever to control two proportional solenoids, for an assigned auxiliary hydraulic valve. The ECM will use a PWM output signal in order to control the amount of electrical current that is sent to the solenoids. When the PWM duty cycle signal from the lever position sensor changes, the ECM adjusts the amount of current that is sent to the solenoids. The current sent to the solenoids determines the amount of pilot oil pressure directed to the hydraulic valve to move the valve spool. An increase in the amount of electrical current that is applied to the solenoids will increase the movement of the valve spool. The movement of the valve spool will result in more hydraulic oil flow to the hydraulic cylinder for the implement. When the lever is in the neutral position, the duty cycle is approximately 50 percent. At this level, the ECM outputs a small current which is not enough to cause the valve spool to move. This small current output to the solenoid enables quicker response time when a move is requested.

Advanced Control Joystick (ACJ) Position Sensors

When the ACJ thumbwheels are configured as Lever 8 and Lever 9 for control of Auxiliary Hydraulic Circuits, the duty cycles will be:

Lever No. 8 - Assigned to the "thumbwheel" on the left-hand ACJ. The sensor signal duty cycle will be approximately 5% to 45% when the "thumbwheel" switch is at the full lower position. The duty cycle will be approximately 55% to 95% when the "thumbwheel" switch is at the full upper position. When the "thumbwheel" switch is in the center position, the duty cycle will be approximately 50% (± 5). The Implement ECM will interpret a duty cycle below 5% as "shorted low" and a duty cycle above 95% as "shorted high/open circuit".

Lever No. 9 - Assigned to the "thumbwheel" on the right-hand ACJ. The sensor signal duty cycle will be approximately 5% to 45% when the "thumbwheel" switch is at the full lower position. The duty cycle will be approximately 55% to 95% when the "thumbwheel" switch is at the full upper position. When the "thumbwheel" switch is in the center position, the duty cycle will be approximately 50% (± 5). The Implement ECM will interpret a duty cycle below 5% as "shorted low" and a duty cycle above 95% as "shorted high/open circuit".

Float ON/OFF Switch - Assigned to the upper push button on the right-hand ACJ. The push button is a "switch to ground" type input.

When the ACJ thumbwheels are configured for Grade Control, the duty cycles will be:

Grade Control Increment/Decrement Switch (Left side) - Assigned to the "thumbwheel" on the left-hand ACJ. The sensor signal duty cycle will be approximately 20% to 45% when the "thumbwheel" switch is at the Decrement position. The duty cycle will be approximately 55% to 90% when the "thumbwheel" switch is at the Increment position. When the "thumbwheel" switch is in the center position or no command, the duty cycle will be approximately 45% to 55%. The Implement ECM will interpret a duty cycle below 5% as "shorted low" and a duty cycle above 95% as "shorted high/open circuit". A duty cycle between 5% and 20% is interpreted as "No Command".

Grade Control Increment/Decrement Switch (Right side) - Assigned to the "thumbwheel" on the right-hand ACJ. The sensor signal duty cycle will be approximately 20% to 45% when the "thumbwheel" switch is at the Decrement position. The duty cycle will be approximately 55% to 90% when the "thumbwheel" switch is at the Increment position. When the "thumbwheel" switch is in the center position or no command, the duty cycle will be approximately 45% to 55%. The Implement ECM will interpret a duty cycle below 5% as "shorted low" and a duty cycle above 95% as "shorted high/open circuit". A duty cycle between 5% and 20% is interpreted as "No Command".

Grade Control Auto/Manual Switch (Left side) - Assigned to the upper push button on the left-hand ACJ. The push button is a "switch to ground" type input.

Grade Control Side Shift Auto/Manual Switch - Assigned to the lower push button on the left-hand ACJ. The push button is a "switch to ground" type input.

Grade Control Auto/Manual Switch (Right side) - Assigned to the upper push button on the right-hand ACJ. The push button is a "switch to ground" type input.

Hydraulic Float Function

A hydraulic float function is available for the auxiliary hydraulic valves that are assigned to auxiliary control lever #1, #4, #6 and #9. Auxiliary control levers #1 and #4 are only available if the auxiliary control pod is installed. If the auxiliary control pod is not installed, stand-alone control lever #6 can be installed along with a stand-alone control lever #7. The mini joystick control cannot be installed independent of the auxiliary control pod. Lever #9 is equipped with a float function on the right-hand ACJ that is activated with a push-button switch.

To enable "Float" functions for auxiliary control levers: The status of the float function needs to be "installed" in the Cat ET configuration screen. This action must be performed when the status of the control lever is "installed".

Control levers #1, #4 and #6 have a "Soft Detent" position on the lever travel. If the lever is moved through the Soft Detent position: The ECM sends a current signal to the assigned proportional solenoids that move the valve spool to the float position. Each control lever has corresponding LED indicators that are located on the control pod. If control lever #6 is installed "stand alone": An LED indicator is installed in the cab to indicate when the lever is in "Float" position. The Implement ECM will illuminate the LEDs when the auxiliary valves are in the float mode.

The power for the LED float indicators is supplied directly from the "Implement Control" fuse. The LED circuits are connected to the Implement ECM sinking driver contacts. The ECM turns ON the sinking circuit for a particular LED in order to provide a ground path and illuminate the LED.

Configuring Auxiliary Hydraulic Control

Machines shipped from the factory with an attachment implement installed have factory-default auxiliary control lever and valve assignments. The Implement ECM can be configured to allow any auxiliary control lever installed on the machine to control any auxiliary hydraulic valve on the machine. The electronic assignment of specific control levers to control specific valves can be accomplished using the AVSpare Electronic Technician (Cat ET) service tool.

Note: When a machine is equipped with an attachment auxiliary hydraulic function: The factory default for the "Auxiliary Control Pod Enable Status" in the configuration menu will be "ENABLED". That happens regardless of whether the Auxiliary Pod Control is, or is not, installed on the machine. The Auxiliary Control Pod Enable Status must remain in the "ENABLED" configuration for the auxiliary hydraulic system to function correctly.

For the procedure of assigning specific control levers to specific valves and a table of the factory default assignments, refer to Testing and Adjusting, UENR3480, "Auxiliary Hydraulic System - Configure".

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