993K Wheel Loader Electrohydraulic System Caterpillar

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Sudden movement or accidental starting of the machine can cause personal injury or death to persons on or near the machine. To prevent personal injury or death, perform the following: Park the machine on a smooth, level surface. Lower the work tool to the ground and engage the parking brake. Stop the engine and remove the key. Block the wheels and install the steering frame lock.

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Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the work tools have been lowered to the ground, and the oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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Right main control valve (front view) (1) Tilt back line relief valve

The line relief valve (tilt back) is located on the front side of the right main control valve. The line relief valve (tilt back) relieves pressure in the head end circuit of the tilt cylinders when the main control valve is in the HOLD position. The line relief valve protects components of the tilt circuit from high pressure. External loads on the bucket may cause these high pressures.

A hydraulic test bench is the most accurate method for testing line relief valves. If it is not practical to use a test bench, then use the following procedure on the machine.

Reference: For the pressure and flow for bench testing this valve, refer to the Service Manual module Specifications, "Relief Valve (Line)" for the machine that is being serviced.

1. Connect Caterpillar ET to the machine. The ET connector is located on the control panel on the right side of the cab.

2. Turn the engine start switch to the ON position.

3. Open the ET software program.

4. When ET has started, start the engine. Run the engine at high idle. Warm the hydraulic oil to normal operating temperature.
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   Illustration 2	g01447460

5. Select "Implement 993K". Press the "OK" button.
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   Illustration 3	g01447462

6. Select "Diagnostic Tests" from the "Diagnostics" menu. Select "Cylinder End Line Relief Pressure Tests".
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   Illustration 4	g01447484

7. When the dialog box appears on the screen, read the information in the dialog box. In order to continue with the test procedure, select the "OK" button.
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   Illustration 5	g01447490

8. When the dialog box appears on the screen, four checked boxes appear. Leave the check mark in the box for each test that will be performed. Select the "Begin" button in order to start the procedure.
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   Illustration 6	g01447422

9. Press the "Next" button in order to begin the procedure. Follow the instructions on the screen. A check mark will appear next to each step as each step is completed.

10. Make sure that the area around the machine is level and clear of obstacles. Keep all personnel away from the machine. Press the "Next" button.

11. Engage the parking brake.

12. Lower the work tool to the ground. Press the "Next" button.

13. Place the steering frame lock in the LOCKED position. Press the "Next" button.

14. Turn the engine start switch to the OFF position.

15. Place the hydraulic lockout switch in the LOCKED position. Press the "Next" button.

16. Adjust the tilt back line relief valve.

    1. Loosen the locknut on the valve.

    2. Turn the adjustment screw by two complete turns in the counterclockwise direction.

    3. Tighten the locknut.

17. Start the engine. Ensure that the parking brake is engaged.

18. Engage the transmission lockout.

19. Place the hydraulic lockout switch in the UNLOCKED position.

20. Warm the hydraulic oil to a temperature of 43 °C (109 °F) or higher. Press the "Next" button.
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    Illustration 7	g01447423

21. Place the tilt control lever in the TILT BACK position until the bucket is fully racked.

22. Place the lift control lever in the LOWER position until the linkage is fully lowered.

23. Run the engine at low idle.

24. Ensure that the lift control lever and the tilt control lever are in the HOLD position. Press the "Next" button.

25. Place the tilt control lever in the TILT BACK position. Hold the lever in the TILT BACK position until the check mark appears on the screen.

26. Place the tilt control lever in the HOLD position. Press the "Next" button.

27. Lower the bucket until the bucket rests flat on the ground. Press the "Next" button.

28. Turn the engine start switch to the OFF position.

29. Place the hydraulic lockout switch in the LOCKED position. Press the "Next" button.

30. If the measured pressure was within the specification, ET will proceed to Step 32. If the pressure was not within the specification, proceed to the next step.
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    Illustration 8	g01447424

31. A dialog box will appear. The box will indicate that the measured pressure is not within the specification. Adjust the tilt back line relief valve. Follow the instructions in the dialog box. After adjusting the valve, press the "OK" button. ET will return to Step 19.

32. If the measured pressure is within the specification, reset the tilt back line relief valve.

    1. Loosen the locknut on the valve.

    2. Turn the adjustment screw by two complete turns in the clockwise direction.

    3. Tighten the locknut.

33. Turn the ignition key to the ON position. Press the "Next" button.
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    Illustration 9	g01447425

34. When the procedure is complete, the "Service Test Successful" message will appear on the screen. In order to exit the program, select the "Finish" button.

35. Turn the engine start switch to the OFF position. Disconnect ET from the machine.