994H Wheel Loader Electrohydraulic System Caterpillar

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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 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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Personal injury or death can result from escaping fluid under pressure. Escaping fluid under pressure, even a very small pin-hole size leak, can penetrate body tissue and cause serious injury and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury. Always use a board or cardboard when checking for a leak.

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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.

Note: This machine is equipped with ECMs for the following: Advisor, Engine, Implement, Transmission, Product Link and VIMS. Diagnostics are displayed on the display screen for Advisor.

Reference: For additional information on the Implement Electronic Control System, refer to System Operation, "Implement Electronic Control System".

Reference: For additional information on troubleshooting the Implement Electronic Control System, refer to Testing and Adjusting, "Troubleshooting Diagnostic Codes".

Problem 1: The pump makes noise and the cylinder rods do not move evenly. There are also air bubbles in the oil.

Probable causes.

• The viscosity of the oil is incorrect.

• The relief valve opens at low oil pressure.

• There is a loose connection of the oil line on the inlet side of the pump.

• The pump has too much wear.

Problem 2: The oil temperature is too high.

Probable causes:

• The machine is being operated above the intended capacity or in ambient temperatures that are too high for the design of the machine.

• The viscosity of the oil is incorrect.

• The setting of the main relief valve is too low. This problem will cause the relief valve to open.

• The pump has too much wear.

• There is a restriction in an oil passage.

• There is a leak in one or more circuits.

• The load on the system is too high. This problem causes the relief valve to open.

• The oil level is low.

• The oil is contaminated.

• The air flow through the oil cooler is too low.

• The oil flow through the oil cooler is too low.

• The hydraulic oil temperature sensor is faulty.

• There is air in the hydraulic oil.

Note: A problem with air in the hydraulic oil must be corrected before the hydraulic system will operate at normal temperatures. There are two conditions that cause air to be in the hydraulic oil:

• Return oil is flowing into the hydraulic oil tank above the level of oil that is in the tank.

• There are leaks in the line between the hydraulic pump and the hydraulic oil tank.

Problem 3: The output of the implement pump is low.

Probable causes:

• The engine power is too low.

• The oil level is low.

• The viscosity of the oil is incorrect.

• The pump has too much wear.

• The pump is not upstroking.

Problem 4: The oil pressure is low.

Probable causes:

• The relief valve opens at low oil pressure.

• The pump has too much wear.

• The control valve and the valve spool have excessive wear.

Problem 5: The work tool moves while the control lever is in the HOLD position.

Probable causes:

• The control valve or the stem in the main control valve have excessive wear.

• There is a leak between the control valve and the cylinder that has drifted.

• A stem in the main control valve is not centering correctly.

• The control lever was not in the HOLD position when the engine start key was turned to the ON position. There may be dirt or the return spring may be broken.

• The lever position sensor has failed.

• The position sensor for the implement control linkage has failed.

• A solenoid on a pilot control actuator has failed.

• The solenoid valve on the pilot control actuator is improperly torqued.

Problem 6: The lift linkage droops when the lift control lever is moved from HOLD position to RAISE position.

Droop - Droop is an initial movement of the hydraulic cylinders in the opposite direction of the selected lever position. The cylinders then move in the correct direction.

Probable causes:

• The makeup valve is not functioning properly.

• The oil is too cold.

• The piston seals and/or the lift cylinders are worn.

• The load check valve is not closing because the spring is weak or broken or because there is dirt or debris in the check valve.

Problem 7: The hydraulic force is too low when the lift control lever is moved to RAISE position or to LOWER position.

Probable causes:

• The engine power is too low.

• The machine is being operated improperly.

• The pilot system pressure is too low.

• The control current to the solenoid is not correct.

• The position sensor for the lift control lever is damaged.

• The main control valve is contaminated or damaged.

• The makeup valve is sticking.

• The pilot control actuator is contaminated or damaged.

• The main relief valve setting is too low.

Problem 8: All implement functions are sluggish.

Probable causes:

• The engine power is too low.

• The oil level is low.

• The pump is worn or damaged.

• The implement electronic control module is not calibrated.

• The main relief valve setting is too low.

• The pilot relief valve is set too low.

• The hydraulic system is contaminated.

Problem 9: The implement functions are erratic or intermittent.

Probable causes:

• The oil level is low.

• The pump has too much wear.

• The implement electronic control module is not calibrated.

• The pilot relief valve is faulty.

• The main control valve is contaminated or damaged.

• The load check valve is not closing because the spring is weak or broken or because there is dirt or debris in the check valve.

• There is air in the hydraulic oil.

Note: A problem with air in the hydraulic oil must be corrected before the hydraulic system will operate at normal temperatures. There are two conditions that cause air to be in the hydraulic oil:

• Return oil is flowing into the hydraulic tank above the level of oil that is in the tank.

• There are leaks in the oil suction line between the pump and the tank.

Problem 10: There is too much lift cylinder drift.

Drift - Drift is the creeping of the implement cylinders while the control is in the HOLD position.

Probable causes:

• The control current to the solenoid is incorrect.

• There are worn parts or damaged parts in the following components: control valve, resolver, pressure relief valve and main relief valve.

• The components of the ride control valve are worn.

• The piston seals and/or the lift cylinders are worn.

• The load check valve is not closing because the spring is weak or broken, or because there is dirt or debris in the check valve.

Problem 11: The hydraulic force is too low when the tilt control lever is moved to TILT BACK position or to DUMP position.

Probable causes:

• The engine power is too low.

• The machine is being operated improperly.

• The position sensor for the tilt control lever is sending an incorrect signal.

• The control current to the solenoid is incorrect.

• The pilot relief valve setting is too low or the valve is faulty.

• The settings of the line relief valves are too low.

• The piston seals and/or the tilt cylinder is worn.

• The main control valve is contaminated or damaged.

• The pilot control actuator is contaminated or damaged.

• The main relief setting is too low.

• The solenoid for the pilot control actuator is torqued improperly.

Problem 12: The cylinder will collapse or the work tool will not raise when the control lever is in the RAISE position.

Collapse - Collapse is a sudden drop of an implement cylinder during normal operation.

Probable causes:

• The lift control lever and/or the position sensor may be worn or damaged.

• The control current to the solenoid is incorrect.

• The float valve is stuck open.

• The solenoid for the pilot control actuator has failed.

• The pilot relief valve is faulty.

• The piston seals and/or the lift cylinders are worn.

• The main control valve is contaminated or damaged.

• The makeup valve is sticking.

• The load check valve is not closing because the spring is weak or broken, or because there is dirt or debris in the check valve.

Problem 13: There is low power to all the implements.

Probable causes:

• The machine is being operated above the intended capacity.

• The engine power is too low.

• The pump has too much wear.

• The pump is not upstroking.

• The control current to the solenoid is incorrect.

• The implement electronic control system is not calibrated correctly.

• The pilot relief valve setting is too low or the valve is faulty.

• The main relief valve setting is too low.

• The settings of the line relief valves are too low.

• The piston seals and/or the cylinders are worn.

• The load check valve is damaged or contaminated.

Problem 14: There is too much tilt cylinder drift.

Drift - Drift is the creeping of the implement cylinders while the control is in the HOLD position.

Probable causes:

• The control current to the solenoid is incorrect.

• The solenoid for the pilot control actuator is torqued improperly.

• The setting of the line relief valve is too low.

• The pilot control actuator is worn or damaged.

• The piston seals and/or the tilt cylinder is worn.

• The components of the main control valve are worn or damaged.

• The load check valve is contaminated or damaged.

Problem 15: The tilt cylinders collapse during the tilt function.

Collapse - Collapse is a sudden drop of an implement cylinder during normal operation.

Probable causes:

• The control current to the solenoid is incorrect.

• The piston seals and/or the tilt cylinder is worn.

• There is dirt or debris in the main control valve.

• The main control valve spool and mating surfaces may be worn or damaged.

• The makeup valve is sticking.

• The float valve is stuck open.

Problem 16: One implement function is sluggish or nonfunctional.

Probable causes:

• The position sensor for the control lever is sending an incorrect signal.

• The control current to the solenoid is incorrect.

• The setting of the line relief valve is too low.

• The main control valve spool and the mating surfaces are worn or damaged.

• A pilot control actuator is sticking.

• A solenoid for the pilot control actuator has failed.

• The float valve is stuck open.

Problem 17: The implements are not functioning.

Probable causes:

• The implement lockout switch is in the LOCKED position.

• The solenoid for the pilot pressure control valve has failed.

• There is no current to the solenoid for the pilot pressure control valve.

• The pilot and braking pump is worn or damaged.

• The main hydraulic pump has too much wear.

• The pilot relief valve setting is too low or the valve is faulty.

• The float valve is stuck open.

• The main relief valve setting is too low.

• The implement electronic control module has failed.

Problem 18: The work tool droops when the tilt control lever is moved from HOLD position to TILT BACK position.

Droop - Droop is an initial movement of the hydraulic cylinder in the opposite direction of the selected lever position. The cylinder will then move in the correct direction.

Probable causes:

• The makeup valve is not functioning properly.

• The oil is too cold.

• The piston seals and/or the tilt cylinders are worn.

• The load check valve is not closing because the spring is weak or broken or because there is dirt or debris in the check valve.