980M and 982M Wheel Loaders Power Train, Steering, Braking, Hydraulic, and Machine Systems Caterpillar

The 980M and 982M machines are equipped with an electro-hydraulically controled steering system. The electro-hydraulic (EH) steering system is standard on the 980M and 982M machines.

Illustration 1	g03663185
Components that make up the steering electrohydraulic system (1) Implement ECM (2) Power train ECM (3) Left Hand Steering Control (4) Brake/Fan combination valve (5) Steering accumulator (6) Secondary steering pump relay (7) Steering Control Valve (8) Steering cylinders (9) Secondary steering diverter valve (10) Secondary steering pump (11) Steering pump (12) Brake/Fan pump (13) Hydraulic tank

Electronic Control

Illustration 2	g03662522
Components that are used for the electronic control of the primary steering system and the secondary steering system (1) Implement ECM (2) Power train ECM (14) Left Armrest Switch (15) Steering Control Spool Position Sensor (16) Steering Pump Pressure Sensor (if equipped) (17) Secondary Steering Pump Pressure Sensor (if equipped) (18) Steering Pilot Solenoid (19) Left and Right Primary Steering Solenoids (20) Feedback Motor Control (21) Steering Control Lever (22) Steering Cylinder Position Sensors (23) Operator Present (24) Left and Right Secondary Steering Solenoids (25) Secondary Steering Pump Relay (26) Data Links

The implement ECM (1) and the power train ECM (2) work together to provide a primary and secondary steering system. The ECMs are located in the cab, behind the operator seat.

The Implement ECM and Power Train ECM communicate over the data links (26). The ECMs use the CAN A Data Link or CAN B Data Link as the primary data links. In the case of a failure, the ECMs will use the Cat Data Link as a backup.

Both ECMs monitor the steering control lever (21) (steering position sensors). The ECMs (both) also monitor steering cylinder position sensors (22), and if the operator is present (23). These inputs are used for steering (articulating) the machine when either the primary steering system is active or when the secondary steering system is active.

The Implement ECM also monitors the left armrest switch (14) and steering control spool position sensor (15). The ECM uses the steering control spool position sensor, along with the steering cylinder position sensors, to ensure the machine articulates in the desired direction. The steering pump pressure sensor (16) and secondary steering pump pressure sensors (if equipped) (17) also provide input to the Implement ECM for the secondary steering pump.

The Implement ECM sends current to the steering pilot solenoid (18) and to the left and right primary steering solenoids (19). The primary steering solenoids are used to articulate the machine. The Implement ECM also controls the feedback motor (20) in the base of the left-hand steering control. The feedback motor provides feedback (resistance) to the operator as the machine is articulated.

The Power Train ECM sends current to left and right secondary steering solenoids (24). The secondary steering solenoids will articulate the machine if either of the primary steering solenoids has an active fault code. The Power Train ECM also energizes the secondary steering pump relay (if equipped) (25) if the steering pump fails or if the engine fails while the machine is moving.

Illustration 3	g03663737
Steering Control Lever (3) Left Hand Steering Control (27) Speed range thumb roller (28) Transmission direction switch

The EH steering system is equipped with a steering control lever (3). The steering control lever combines the steering functions and the transmission functions for the machine. Move the control to the left or to the right to articulate the machine.

The transmission direction switch (28) is located on the front of the control. The transmission direction switch allows the operator to choose the machine direction. The speed range thumb roller (27) is located near the top of the steering control lever. The thumb roller allows the operator to select the transmission speed.

Illustration 4	g03556959
Steering control lever connections

The steering function uses hall cell type sensors that send PWM signals to the Implement ECM and to the Power Train ECM. This image shows the electrical connections between the steering control lever, the Implement ECM, and the Power Train ECM.

The steering control lever contains three steering sensors that are necessary for correct steering operation. All three sensors send a PWM signal to both the Implement ECM and the Power Train ECM. Steering sensors 1 and 2 are powered from the Implement ECM. Steering sensor 3 is powered from the Power Train ECM.

A Level 3 Warning occurs when any steering lever position sensor fails. The machine will continue to articulate normally (with an active Level 3 warning) using the two remaining sensors.

The steering control lever also contains the feedback motor. The feedback motor aligns the control with the machine articulation angle if all of the conditions have been met. The feedback motor also provides feedback (resistance) to the operator when the operator articulates the machine.

The Implement ECM compares the position of the steering control lever to the machine articulation angle. The amount of resistance the feedback motor produces is determined by the difference between the machine articulation angle and the steering control lever position. The larger the difference between the machine articulation angle and the steering control lever position, the greater the resistance will be.

If the steering control lever is released in the desired position when there is resistance, the steering control lever will move in the direction of the resistance until the control aligns with the articulation angle of the machine. If the steering control lever is released in a desired position when there is no resistance, the steering control lever will remain in that position.

A Level 3 Warning occurs when the feedback motor has a fault code or is not responding to the commands from the Implement ECM. The machine will continue to articulate normally (with an active Level 3 warning), but the operator will not receive feedback from the steering control lever.

There are some points to consider when diagnosing Failure Mode Indicators (FMI) for the steering lever position sensors:

• Verify that 8 V power supply for the Implement ECM does not have any active codes. Correct any problems with the 8 V power supply if any diagnostic codes are active.

• Verify that 8 V power supply for the Power Train ECM does not have any active codes. Correct any problems with the 8 V power supply if any diagnostic codes are active.

• The Implement ECM and the Power Train ECM receive an input signal from the steering position sensors. Both ECMs can activate a diagnostic code for all three sensors. Most likely the sensor is operating correctly if one ECM has activated a diagnostic code and the other ECM has not. When this situation occurs, a poor connection in the machine harness would be suspected. When both ECMs have activated the diagnostic code, either the sensor or a harness problem could be the cause. That both ECMs have failed when both ECMs have activated the diagnostic code is unlikely.

Steering and Transmission Control (Left Joystick) Auto Alignment

After the machine conditions that are listed above are met, the Implement ECM will activate the ON/OFF output to enable the joystick force feedback motor. The ECM will determine the articulation angle of the machine based on the Pulse Width Modulated (PWM) signals from the left and right articulation cylinders.

The ECM will then send PWM torque commands to the electronics in the joystick that control the force feedback motor. Based on the torque commands from the ECM, the motor will be commanded to move the joystick to the position that corresponds to the articulation angle of the machine.

The auto alignment function generally requires a short time period of a few seconds to complete.

When the auto alignment procedure is successfully completed, the Implement ECM will energize the ON/OFF circuit for the Steer Pilot Supply Solenoid. This solenoid is located on the Steering Control Valve. When the solenoid is energized, pilot hydraulic oil will be supplied to the left and right steer solenoid valves on the control valve. The steering system will be enabled.

Once enabled, the articulation angle will follow the movement of the joystick. The steering system alert indicator will turn OFF and the E562 (Steering System Not Aligned with Angle) event will no longer be active.

The Implement ECM will report that the steering system is enabled on the CAN A Data Link and the CAT Data Link communication systems.

Note: If ground speed is greater than zero, the ECM will attempt to align the joystick to the machine angle. The ECM will enable steering when alignment is complete or 2 seconds after machine travel is detected.

Unsuccessful Auto Alignment

The following conditions can cause the Implement ECM to either extend or abort the joystick auto alignment function:

• The joystick cannot move freely through the full left/right steering axis. The cause could be either interference by an operator or contact with an object in the axis sweep path. Do not allow anyone or anything to interfere with the free movement of the joystick.

• Activation of any of the following force feedback motor diagnostic codes: CID 2865 (Steering Control Force Feedback Motor Enable Output), CID 2865 (Steering Control Force Feedback Motor Torque Sensor), CID 3082 (Steering Control Force Feedback Motor).

• Active diagnostic codes for the position sensor circuits on both articulation steering cylinders (CID 2200 - Left Cylinder, CID 2201 - Right Cylinder). These diagnostic codes could be activated by the Implement ECM and / or the Machine ECM.

• High 24 VDC system control voltage. A CID 168, FMI 03 (System Voltage Above Normal) diagnostic code will be active on several of the control modules on the machine when this condition is present.

• If all required machine conditions are met and the force feedback motor is not enabled, the auto alignment will be unsuccessful. In this case, a manual alignment procedure can be performed.

Steering and Transmission Control (Left Joystick or Optional Steering Wheel) Manual Alignment

Note: Manual alignment of the Left Hand Steering Control (Left Joystick) or optional steering wheel should only be attempted when the auto alignment function is not successful and the machine must be moved a short distance. An unsuccessful auto alignment indicates that there is a problem in the steering system. Investigate and resolve the problem that is preventing the auto alignment before resuming normal machine operation.

When the joystick or optional steering wheel is manually aligned, the force feedback motor may or may not be enabled depending on system conditions.

As with the auto alignment procedure, the Implement ECM will not allow manual alignment of the joystick or optional steering wheel until the required machine conditions are met.

The operator status must be “present”, left console in the down position with the engine in operation. The parking brake must be ON and the transmission must be in NEUTRAL.

Note: If the optional steering wheel is equipped on your machine, the left armrest position switch enabled condition will NOT apply.

The Transmission ECM will not allow the parking brake to be released or a transmission directional shift out of NEUTRAL until the Implement ECM enables the steering system.

Once the machine conditions are satisfied, the alert indicator for the steering system on the monitoring system display will be illuminated. In addition the Implement ECM will activate an E562 (Steering System Not Aligned with Angle) event.

The following steps must be followed to manually align the left joystick or optional steering wheel to the articulation angle:

1. Move the left joystick or optional steering wheel to the approximate position that corresponds to the articulation angle of the machine.

2. Slowly move the left joystick or optional steering wheel a small amount of travel to the left and / or right to activate alignment and steering control.

3. Once the ECM detects that the joystick or optional steering wheel position is aligned with the articulation angle, the articulation angle will follow the movement of the joystick or the optional steering wheel. The steering system will be enabled. The alert indicator and the active steering event will be deactivated.

If the ECM does not enable the steering control:

• Check for active diagnostic codes. The same fault conditions that can prevent auto alignment can prevent manual alignment of the joystick or optional steering wheel. The diagnostic codes that will prevent alignment are listed in the auto alignment section.

• Slightly expand the left or right sweep of the joystick or optional steering wheel in slow steady movement. The joystick or optional steering wheel should not be swept to the full left or right positions.

• If the machine is articulated to the full left or right position and the ECM will not align the joystick or optional steering wheel, it may be necessary to use external force to decrease the machine articulation angle.

Once the ECM detects that the joystick or optional steering wheel position is aligned with the articulation angle, the Implement ECM will enable steering.

Steering Enabling Override

The Implement ECM will employ the following logic to enable the steering system when unexpected conditions occur:

• When the machine is moving and steering system is disabled due to a fault condition, the ECM will disregard the normal condition requirements for enabling the system. The ECM will immediately initiate and complete the auto alignment function to restore steering operation within a few seconds.

• If the machine is moving and the steering operation has been disabled due to a force feedback motor fault condition, the ECM will allow joystick operation without the resistive force feedback being activated. In this case, the Implement ECM will move the machine articulation angle to alignment with the joystick.

• Once the machine is stopped (zero speed), the steering system operation will be disabled. A manual joystick or alignment will have to be performed in order to move the machine.

If any of these conditions occur, safely stop machine operation at the earliest opportunity. Only operate the machine long enough to move to a secure location or to a repair location. Determine the cause of the problem and resolve the problem before normally operating the machine.

Disabling Steering

Once enabled, the steering system will remain enabled until the Implement ECM detects the following conditions:

• Machine speed is zero.

AND

• Actual Gear is NEUTRAL.

AND

• EITHER the left armrest is raised as reported by the Armrest Position Switch OR the operator is not in the seat as indicated by the operator present logic. (Refer to “Operator Present Sensor, Operator Present Logic” in this section.) Note: If the optional steering wheel is equipped on your machine, the left armrest position switch enabled condition will NOT apply.

OR

• Machine speed is zero and the key start switch is moved to the OFF position.

Steering Disable Override

If a situation occurs when the machine is moving that would normally cause steering to be disabled, the Implement ECM will continue steering operation until travel speed is zero.

If the machine is moving and a force feedback motor fault condition occurs, the ECM will continue steering control without the resistive force feedback on the joystick or optional steering wheel.

Once the machine is stopped (zero speed), the steering system operation will be disabled. The condition that caused the system to be disabled will have to be resolved before the ECM will enable steering operation.

Steering Pump and Pilot Oil

Illustration 5	g03659629
Steering pump and pilot pump (parts removed for clarity) (4) Brake/Fan combination valve (11) Steering pump (12) Brake/Fan/Pilot pump

Illustration 6	g03663755
Brake control valve schematic (P1) To steering control valve (Redundant Supply) (P2) Pilot supply to steering control valve (SP) From steering pump supply (T) Tank (4) Brake/fan combination valve (12) Brake/Fan pump (27) Reducing valve (28) Shuttle valve (29) Reducing valve (30) Brake system relief valve

The brake and fan pump (12) is mounted to the front gear train of the engine. The brake fan supplies oil to the brake system, fan system, and pilot oil to the steering control valve.

The steering pump (11) on the 980M and 982M machines is mounted to the implement pump on the right side of the machine. The variable displacement piston pump senses both pressure and flow requirements for the system. The steering system pump draws oil from the hydraulic tank through the suction tube. The pump then sends flow through the supply hose to the steering control valve.

Pilot oil for the steering control is supplied by brake/fan pump (12) and brake/fan combination valve (4) reduces oil for the primary steering valves through port (P2). Valve (27) reduces oil pressure for the secondary (redundant) steering valve through port (P1).

If a failure occurs with the brake pump supply pressure, shuttle valve (28) will shift left under spring pressure. The oil in (SP) will flow through the shuttle to reducing valve (27). This oil will flow to the secondary solenoid valves for secondary steering. Refer to System Operation, "Steering Pilot System" for additional information on the pilot system.

Illustration 7	g03662457
(4) Brake/Fan combination valve (29) Pressure Reducing Valve (27) Pressure Reducing Valve

The brake/fan combination valve (4) is located in the service center on the right side of the machine. Pressure reducing valve (29) provides the pilot oil supply to the pilot steering solenoid and the primary steering solenoids in the steering control valve. The pressure reducing valve (29) provides the pilot oil supply to the secondary steering solenoids in the steering control valve. The pressure reducing valve (29) also provides pilot oil to the implement pilot lockout solenoid.

Illustration 8	g03662478
(5) Steering Pilot accumulator

The steering pilot accumulator (5) is mounted on the top of the steering control valve that is mounted to the front of the transfer case on the 980M and 982M machines. The accumulator stores the pilot supply oil during normal operation and provides a temporary supply of pilot oil if a loss of pump flow occurs.

Steering Control Valve and Steering Operation

Illustration 9	g03562402
Steering control valve and components (1) Steering control valve (2) Back-up relief valve (3) Crossover relief and makeup valve (4) Left secondary steering solenoid (5) Right secondary steering solenoid (6) Right primary steering solenoid (7) Steering pilot ON/OFF solenoid (8) Left primary steering solenoid (9) Crossover relief and makeup valve (10) Steering control spool position sensor

The steering control valve (1) is mounted to the transmission transfer gears near the articulation hitch. The steering control valve directs supply oil from the steering pump to the steering cylinders. Components located on the steering control valve are listed in Illustration 9.

Illustration 10	g03562416
Steering Control Valve (Primary Steering - No turn) (1) Steering control valve (2) Back-up relief valve (3) Crossover relief and makeup valve (4) Left secondary steering solenoid (5) Right secondary steering solenoid (6) Right primary steering solenoid (8) Left primary steering solenoid (9) Crossover relief and makeup valve (10) Steering control spool position sensor (11) Oil from brake/fan combination valve (12) Oil from steering pilot solenoid (13) Right turn port (14) Tank port (15) Load signal to pump (16) Supply oil (17) Left turn port (18) Steering control spool

When the left-hand steering control is in the HOLD position and no turn is requested, pilot oil flow to either end of the steering control spool (18) is blocked by the left and right primary steering solenoids (6) and (8).

With no pilot oil present at either end of the steering control spool, the centering springs keep the spool in the centered position. When the spool is centered, the spool blocks supply oil (16) from the steering pump to the right turn port (13) and left turn port (17). The spool also blocks the oil from the steering cylinders from the tank port (14).

Illustration 11	g03562417
Steering Control Valve (Primary Steering - Right turn) (2) Back-up relief valve (3) Crossover relief and makeup valve (4) Left secondary steering solenoid (5) Right secondary steering solenoid (6) Right primary steering solenoid (11) Oil from brake/fan combination valve (12) Oil from steering pilot solenoid (13) Right turn port (14) Tank port (15) Load signal to pump (16) Supply oil (17) Left turn port (18) Steering control spool (19) Resolver valve (20) Back pressure valve (21) Resolver valve

When the left-hand steering control is moved to the RIGHT TURN position, pilot oil flows from the right primary steering solenoid (6) to the resolver valve (19) and to the right end of the steering control spool (18). The pilot oil pressure moves the spool to the left.

When the spool moves to the left, supply oil (16) flows past the spool to the right turn port (13). Oil flows to the head end of the left steering cylinder and to the rod end of the right steering cylinder. At the same time, a load signal (15) is sent through the resolver valve (21) to upstroke the steering pump.

Oil from the head end of the right steering cylinder and oil from the rod end of the left steering cylinder flows into the left turn port (17), through the back pressure valve (20), and to the tank port (14). The machine articulates to the right.

The steering control valve has a back-up relief valve (2) to limit the maximum pressure in the steering system if the pressure compensator spool of the steering pump fails.

When the left-hand steering control is released, pilot oil is blocked by the right primary steering solenoid. Oil pressure present at the right end of the steering control spool flows through the right primary steering solenoid and to the tank. Spring force causes the spool to return to the center position.

When the left-hand steering control is in the HOLD position, the steering control spool blocks oil flow to the steering cylinders, which keeps the machine in the RIGHT TURN position.

If an outside force tries to turn the machine with the steering control spool in the center position, oil pressure in the steering cylinders will increase. This pressure increase opens the crossover relief and makeup valve (3).

The operation for the secondary steering solenoids (4) and (5) is the same as the primary steering solenoids.

Steering Cylinders

Illustration 12	g03664841
Steering cylinder location (22) Steering cylinders (left side shown) (22F) Front (Rod end) of cylinder (22)

The steering cylinders (22) are located on the sides of the machine. The steering cylinders have an internal position sensor (not shown) which allows the Implement ECM and the Power Train ECM to monitor the steering position of the steering cylinders. This signal is compared to the position of the left-hand steering control sensors for diagnostic purposes

When a steering cylinder is changed, a steering cylinder calibration routine must be performed using Cat ET.

Note: The steering cylinder position sensors are powered from two different ECMs. The left sensor is powered from the Power Train ECM and the right sensor is powered from the Implement ECM.

Illustration 13	g03562419
Steering cylinder sensors (23) Sensor head (24) Magnet (25) Sensor rod

The steering cylinders are equipped with position sensors. The sensor sends a Pulse Width Modulated (PWM) signal to the ECM indicating the cylinder piston position within the piston stroke.

The sensor uses the magnetostrictive principle. A wire is stretched inside the length of the sensor rod (25) in order to form a waveguide. At time zero, a current pulse is transmitted down the wire by the electronics in the sensor head (23). At the point where the pulse reaches the magnetic field of the magnet (24), noise is generated and sent back to the sensor head. Internal electronics converts the time zero to the elapse time for the noise to reach the sensor head into a PWM signal. The pulse width is directly proportional to the position of the magnet. The sensor frequency is approximately 500 Hz.

Steering Operation (Electronic Control)

Illustration 14	g03562421
Primary steering control (1) Implement ECM (2) Steering pilot solenoid (3) Right primary steering solenoid (4) Left primary steering solenoid (5) Transmission output speed (from power train ECM) (6) Steering cylinder position sensors (7) Data Links (8) Power Train ECM (9) Left-hand steering control (10) Operator present (11) Feedback motor control (12) Steering pump pressure sensor (If equipped) (13) Left armrest switch (14) Steering control spool position sensor

The primary steering operation is controlled by the Implement ECM (1). The Implement ECM uses input components, output components, and information from the Data Links (7) to control the steering control valve.

Inputs for the Implement ECM include:

• Transmission Output Speed (TOS) from Power Train ECM (5)

• Operator present switch (10)

• Left armrest switch (13)

• Left-hand steering control (9)

• Steering control spool position sensor (14)

• Steering cylinder position sensors (6)

• Steering pump pressure sensor (if equipped (12))

Outputs for the Implement ECM include:

• Steering pilot solenoid (2)

• Right primary steering solenoid (3)

• Left primary steering solenoid (4)

• Command signal to the feedback motor control (11)

The Implement ECM will align the left-hand steering control with the machine articulation angle once all of the setup conditions are met. The conditions are as follows:

• Engine must be operating

• Transmission Output Speed (TOS) is 0 rpm

• Operator must be present

• Left armrest must be in the DOWN position

When all of the conditions have been met, the Implement ECM will command the feedback motor to align the left-hand steering control with the machine angle.

The Implement ECM compares the left-hand steering control position sensors to the steering cylinder position sensors. The Implement ECM then commands the feedback motor to align the control with the machine angle.

The feedback motor also provides feedback to the operator when the machine is operating. The Implement ECM compares the desired machine angle to the actual machine angle and provides feedback (resistance) as the machine is articulated. The amount of feedback the operator feels is based on desired machine angle, actual machine angle, machine speed, and hydraulic oil temperature.

The Implement ECM sends current to the left primary steering solenoid or right primary steering solenoid that direct pilot oil to move the steering control spool. The spool then directs supply oil to the steering cylinders and the steering cylinders will move in the desired direction.

The Implement ECM will monitor the position of the steering cylinders as well as the steering control spool position sensor. The Implement ECM will decrease the current to the primary steering solenoids as the steering cylinders approach the desired position. When the machine speed is over 7 km/h (4. mph), the Implement ECM will only use the steering cylinder position sensors to monitor the articulation angle of the machine.

The steering system is speed sensitive and as the machine speed increases, the steering sensitivity will be reduced. The Implement ECM will receive information from the data links and adjust the steering sensitivity.

The steering system is also temperature sensitive. If the hydraulic oil temperature is below −10° C (14° F), the machine will be placed in the steering cold mode. The machine will be limited to SECOND FORWARD or SECOND REVERSE and the operator will experience higher feedback (resistance) when steering the machine.

If there is a fault with any of the primary steering system components, the Power Train ECM (8) will activate the secondary steering system.

The Implement ECM will send a PWM signal to the Power Train ECM if the secondary steering system needs to be activated due to a secondary steering test or a problem in the primary steering system. The duty cycle of the PWM signal will be used to determine which specific c secondary steering component needs to be activated. The PWM duty cycle is as follows:

• 20 percent PWM duty cycle: Normal operation, no request to activate.

• 40 percent PWM duty cycle: Request to activate the secondary steering pump (if equipped) only.

• 60 percent PWM duty cycle: Request to activate the secondary steering pilot solenoid valves only.

• 80 percent PWM duty cycle: Request to activate the secondary steering pump (if equipped) and the secondary steering solenoid valves.

The steering system will be disabled when the following conditions occur:

• Transmission Output Speed (TOS) is 0 rpm

• Actual gear is NEUTRAL

• Operator is NOT present

Operator In Seat Sender, Operator Present Logic

The Operator Present Sender is embedded in the seat cushion of the operator seat. The sender is made up of a number small pressure sensors that are arranged in a pattern in the center and forward portions of the seat cushion. The sensors are parallel connected to the two sender circuits. If an individual sensor fails, the signal to the ECM is not interrupted.

Changing pressure on the sensors will result in a change in the circuit resistance that the ECM detects. A voltage can be measured between the sensor circuits that will correspond to the resistance of the circuit.

The sender resistance range is 90 ohms (0.2 VDC) to 4000 ohms (4.95 VDC).

The Implement ECM expects to detect a signal circuit resistance of between 90 ohms (0.2 VDC) to 800 ohms (3.2 VDC) when an operator IS in the seat.

The ECM will determine that an operator is NOT in the seat when the signal circuit resistance is between 800 ohms (3.2 VDC) to 4000 ohms (4.95 VDC).

If the ECM detects a circuit resistance that is above or below the sensor resistance range, a CID 2113 (Operator in Seat Switch) diagnostic code will be activated.

The sender is not serviceable. If the sender has failed, the seat cushion with the embedded sender must be replaced.

In addition to the operator present sender, the ECM will also use other machine conditions to determine if an operator is present.

The Implement ECM will use ANY ONE of the following conditions to determine if an operator IS present:

• The Operator In Seat Sender indicates that an operator is in the seat.

OR

• Machine travel speed IS GREATER THAN ZERO as reported by the Transmission ECM (transmission output speed sensor).

OR

• The active gear is NOT NEUTRAL as reported by the Transmission ECM.

OR

• The service brake pedal IS DEPRESSED more than 10 percent as reported by the Transmission ECM (service brake position sensor).

If any one of the conditions listed above is true, the ECM will determine that an operator is present.

The Implement ECM will use the following conditions to determine if an operator IS NOT present:

• The Operator In Seat Sender indicates that an operator IS NOT in the seat.

AND

• Machine travel speed IS ZERO as reported by the Transmission ECM (transmission output speed sensor).

AND

• The active gear IS NEUTRAL as reported by the Transmission ECM.

AND

• The service brake pedal is NOT DEPRESSED more than 10 percent as reported by the Transmission ECM (service brake position sensor).

OR

• ALL four of the sensors that are reporting the above conditions are faulted.

If ALL of the first four listed conditions listed above are true, the ECM will determine that an operator IS NOT present.

In addition, if diagnostic codes are active for all four of the involved sensors, the ECM will determine that an operator IS NOT present.

The Implement ECM will report the operator present status on the CAN A Data Link and the CAT Data Link communication systems.

Armrest Position Switch

Note: On machines with left joystick only. Machines with steering wheel does not have an armrest position switch.

Illustration 15	g02282613
Armrest position switch as viewed with the armrest in the raised position

The Armrest Position Switch is located under the left armrest toward the rear of the armrest base.

The Armrest Position Switch is used as a machine interlock device. The engine will start with the left armrest in the UP position, however, the Implement ECM will not enable steering operation until the armrest is in the DOWN position.

The switch provides two switch-to-ground inputs to the Implement ECM and the Machine ECM. A ground circuit is supplied to the switch by the Implement ECM.

When the normally closed input circuit is grounded, the ECM determines that the armrest is in the UP position. When the normally open input is grounded, the ECM determines that the armrest is in the DOWN position.

Each ECM expects to detect one switch circuit grounded at all times. If both switch circuits are grounded or if neither switch circuit is grounded, either one or both ECMs could activate a CID 1628 (Armrest Stowed Switch) diagnostic code.

Note: If the optional steering wheel is equipped on your machine, the left armrest position switch enabled condition will NOT apply.

Steering Operation (Hydraulic)

Illustration 16	g03562423
Steering Hydraulic System (HOLD) (1) Steering Pump (2) Steering control valve (3) Backup relief valve (4) To brake/fan combination valve (5) Back pressure valve (6) Makeup and relief valve (7) Makeup and relief valve (8L) Left side steering cylinder (8R) Right side steering cylinder (9L) Left secondary (redundant) steering solenoid (9R) Right secondary (redundant) steering solenoid (10) Pilot oil from brake/fan combination valve (redundant) (11) Pilot accumulator (12) Pilot oil supply from brake/fan combination valve (13) Steering pilot solenoid (14L) Left primary steering solenoid (14R) Right primary steering solenoid (15) Steering control spool

The steering pump (1) provides flow to the steering control valve (2). Supply oil will enter the steering control valve and flow to the steering control spool (15).

Pump supply oil is blocked when the control spool is in the HOLD position. Oil in the load sense circuit is blocked by the steering cylinders (8L) and (8R), and the pump control valve. Pump supply oil is also sent to the brake/fan combination valve (4) to provide a secondary source of pilot oil in the event of a brake/fan pump failure.

The steering control valve contains a back-up relief valve (3) and a back pressure valve (5). The back-up relief valve limits the maximum pressure in the steering control valve if the pressure compensator spool of the steering pump fails. The back pressure valve restricts the return oil flow to the hydraulic tank. The purpose of the back pressure valve is to maintain enough pressurized oil in an internal passage to prevent steering cylinder voiding.

The brake/fan combination valve contains two pressure reducing valves that supply pilot oil to the steering control valve. The pilot oil (12) is supplied to the pilot accumulator (11), steering pilot solenoid (13), and primary steering solenoids (9L) and (9R). Secondary steering solenoids (14L) and (14R) receive a redundant pilot oil supply (10) from the brake/fan combination valve. For additional information about the pilot oil, refer to System Operation, "Steering Pilot System".

The primary steering solenoids meter the amount of pilot oil that is sent to the control spool in the steering control valve. The amount of oil that is sent to the steering control valve is based on the amount of current sent to the primary steering solenoid. The primary steering solenoids are an output of the Implement ECM.

The secondary steering solenoids are used as a back-up in case the primary steering solenoids fail. The secondary steering solenoids meter the amount of pilot oil that is sent to the control spool in the steering control valve. The amount of oil that is sent to the steering control valve is based on the amount of current sent to the secondary steering solenoid. The secondary steering solenoids are an output of the Power Train ECM.

The relief and makeup valves (6) and (7) protect the steering cylinders for sudden pressure spikes. The crossover relief and makeup valves will dump oil from one side of the cylinder to the other if the pressure in the steering cylinders raises above the setting of the relief valves.

Illustration 17	g03562424
Steering Hydraulic System - Primary Steering (RIGHT TURN) (1) Steering Pump (4) To brake/fan combination valve (8L) Left side steering cylinder (8R) Right side steering cylinder (10) Pilot oil from brake/fan combination valve (redundant) (12) Pilot oil supply from brake/fan combination valve (13) Steering pilot solenoid (14R) Right primary steering solenoid (15) Steering control spool (16) Resolver valve (17) Resolver valve (18) Steering control spool position sensor

The Implement ECM receives a request from the left-hand steering control to steer the machine to the right.

The Implement ECM sends a current, based on the request, to the primary right steering solenoid (14R). The right steering solenoid is energized and pilot oil flows through the resolver valve (17) to the control spool (15). The control spool will shift upward and direct pump supply oil to the steering cylinders (8L) and (8R).

The steering control spool position sensor (18) sends a signal to the Implement ECM indicating the directional control spool has shifted. The Implement ECM also monitors the steering cylinder position sensors to ensure that the machine has articulated in the desired direction.

As the machine begins to articulate, the resolver valve (16) sends a load signal to the steering pump (1). The load signal upstrokes the steering pump to meet the demand of the system.