574B Forwarder Hydraulic System Machine System Troubleshooting Caterpillar


Machine System Troubleshooting
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1.1. Problem List
2.1. Probable Causes
3.2. Problem 1
4.3. Probable Causes
5.2. Problem 2
6.3. Probable Causes
7.2. Problem 3
8.3. Probable Causes
9.2. Problem 4
10.3. Probable Causes
11.2. Problem 5
12.3. Probable Causes
13.2. Problem 6
14.3. Probable Causes
15.2. Problem 7
16.3. Probable Causes
17.2. Problem 8
18.3. Probable Causes
19.2. Problem 9
20.3. Probable Causes
21.2. Problem 10
22.3. Probable Causes
23.2. Problem 11
24.3. Probable Causes

------ WARNING! ------

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 attachments have been lowered, 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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NOTICE

Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.

Refer to Special Publication, NENG2500, "AVSpare Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on AVSpare products.

Dispose of all fluids according to local regulations and mandates.


Each of the valves have poppets which act as load check valves. The poppets close the ports so there is almost zero drift of the work tools.

The relief valves in the auxiliary circuit and in the tilt circuit protect the components from pressures in the circuits when the control valves are in the HOLD position.

  • The oil pressure for opening the relief valves for the main system and for the auxiliary circuits must be within the specifications. Pressures that are too low will cause a decrease in the lifting force and in the grapple characteristics. Pressures that are too high will cause a decrease in the life of hoses and of other components.

  • Circuit drift is caused by leakage past cylinder pistons, past O-ring seals in the control valves, past check valves that do not seat correctly or past makeup valves that do not seat correctly. Poor adjustments of the control valves or incorrect fit may also contribute to circuit drift.

If the basic tests indicate a leak in the circuit, install a flow meter and perform a test.

Problem List

Note: Many of the following problems can create diagnostic codes or fault codes in IQAN. These codes can help find the root cause of the problem. IQAN should be used to retrieve the logged codes and active codes.

  1. The hydraulic power is low.

  1. None of the functions will operate or all of the functions operate slowly.

  1. The pilot oil pressure is low.

  1. The piston pump (implement) will not reach maximum output pressure.

  1. The standby pressure cannot be adjusted correctly.

  1. A hydraulic circuit is hammering.

  1. You cannot lower the boom.

  1. You cannot raise the boom or you cannot lower the boom.

  1. You cannot operate the grapple.

  1. The oil temperature is too high.

  1. There are air bubbles in the oil.

Probable Causes

Problem 1

The hydraulic power is low.

Probable Causes

  1. Ensure that the engine is operating correctly.

  1. The hydraulic oil is low. Check the hydraulic oil level.

  1. The oil is not to the correct operating temperature. Check the oil temperature.

  1. There is air bubbles in the oil.

  1. The pilot oil pressure is low.

  1. The maximum pump output pressure is low. Refer to "Problem 4".

  1. The line relief valves are not set correctly.

  1. Pilot control valves do not operate correctly.

  1. The cylinders are leaking.

Problem 2

None of the functions will operate or all of the functions operate slowly.

Probable Causes

  1. The operating mode switch is not in the WORKING MODE position. Place the operating mode switch in the WORKING MODE position.

  1. There is a leak in the system. Visually inspect the system for leaks in the system.

  1. The pilot oil pressure is low.

  1. The high pressure cutoff of the piston pump (implement) for the work tool is not correct.

  1. The standby pressure is not set correctly.

  1. The line relief valves are not set correctly.

  1. The inlet screen for the piston pump (implement) is dirty. Drain the hydraulic tank. Inspect the inlet screen for contamination.

  1. The pilot control valves are not operating correctly.

  1. The seals in the cylinders are leaking.

  1. The implement valve is not operating correctly. Inspect the components of the valve for damage or for contamination.

Problem 3

The pilot oil pressure is low.

Probable Causes

  1. The setting for the pressure reducing valve is not correct.

  1. Check the operation of the pilot relief valve.

  1. The pressure reducing valve is contaminated. Loosen the adjusting screw on the pressure reducing valve and turn the screw inward.

Problem 4

The piston pump (implement) will not reach maximum output pressure.

Probable Causes

  1. The oil level is low.

  1. The viscosity of the oil is incorrect.

  1. The oil is contaminated.

  1. There is air in the oil. Refer to "Problem 11".

  1. The cutoff spool is stuck. Loosen the adjusting screw for the cutoff spool and attempt to readjust the high pressure cutoff.

  1. A ball resolver in the signal network is stuck.

  1. The piston pump (implement) may be worn.

  1. The pressure reducing valve for the maximum signal pressure may have a malfunction.

Problem 5

The standby pressure cannot be adjusted correctly.

Probable Causes

  1. The flow compensator spring that is located in the piston pump (implement) control valve is damaged. Remove the spring and inspect the spring for damage.

  1. The flow compensator spool has damage or the spool has contamination. Remove the spool and inspect the spool.

Problem 6

A hydraulic circuit is hammering.

Probable Causes

  1. There is air in the system. Refer to "Problem 11".

  1. You are not using the machine correctly.

  1. The line relief valves are not set correctly.

  1. The standby pressure is not correct.

  1. The pilot pressure is not set correctly.

Problem 7

You cannot lower the boom.

Probable Causes

  1. There is a loss in pilot pressure.

  1. The spool cannot shift.

  1. The boom lower solenoid has failed.

Problem 8

You cannot raise the boom or you cannot lower the boom.

Probable Causes

  1. None of the other functions are operating correctly. Refer to "Problem 2".

  1. The lift cylinder has damage. Replace the cylinder.

  1. The mechanical linkage of the boom has damage. Repair the damage.

  1. The pilot control valve is not working correctly.

  1. There is a failure in one of the seals of the lift cylinder.

  1. The main control spool is stuck. Disassemble the valve. Inspect the main control spool and inspect the springs.

  1. The area control spools in the lift control valve are stuck. Disassemble the valve. Inspect the area control valves and inspect the springs.

Problem 9

You cannot operate the grapple.

Probable Causes

  1. None of the other functions are operating correctly. Refer to "Problem 2".

  1. The cylinders have damage. Repair the damage.

  1. The line relief valves or the implement valve are not operating correctly. Check the settings for the line relief valves.

  1. The pilot control valve is not working correctly.

  1. The seals in one of the cylinders are leaking.

  1. The main control spool is stuck. Disassemble the valve. Inspect the main control spool and inspect the springs.

Problem 10

The oil temperature is too high.

Probable Causes

  1. The oil level is low.

  1. The hydraulic oil cooler is plugged. Inspect the hydraulic oil cooler and clean the hydraulic oil cooler.

  1. There is air in the hydraulic oil. Refer to "Problem 11".

  1. The viscosity of the oil is incorrect.

  1. The settings for the relief valve are too low.

  1. The oil is contaminated. Replace the filter. Remove the cap from the hydraulic oil tank and inspect the sump screen.

Problem 11

There are air bubbles in the oil.

Note: A problem with air in the hydraulic oil must be corrected before the hydraulic system will operate at normal temperatures.

Probable Causes

  1. There is a loose connection on the oil line on the inlet side of the pump. Visually inspect the supply lines of the pump for leaks and repair the leaks.

  1. Return oil flows into the hydraulic tank above the level of oil that is in the tank. The oil level is low.

  1. The cylinders are cavitating because the back pressure valve is not maintaining pressure in the return passages in the bank valve.

  1. A makeup valve in the lift control valve or the tilt control valve is not opening. Inspect the lines that connect the bank valves to the cylinders for damage.

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