Hot hydraulic oil under high pressure can remain in the components of the hydraulic system or the power train system after the engine has been stopped. The uncontrolled release of the hydraulic oil can cause sudden machine movement and can also result in the following conditions:
If hydraulic oil penetrates body tissue, the injury must be treated immediately by a doctor who is familiar with this type of injury. Use a board or a piece of cardboard to check for a hydraulic oil leak. Make sure that all of the attachments have been lowered to the ground and that all trapped pressure has been released from the hydraulic system and the power train system. Also, make sure that the hydraulic oil is cool before the removal of any components or lines. Remove the hydraulic oil filler cap only when the engine is stopped and the filler cap is cool enough to touch with your bare hand. |
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. |
NOTICE |
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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, PERJ1017, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat® products. Dispose of all fluids according to local regulations and mandates. |
Pilot Pressure - Low Idle | |
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Steering /Brake Pilot System Pressure | |
Implement System Pilot System Pressure | |
There are two pilot systems that are generated from the accumulator charging valve in the hydraulic service center.
- The primary steering pilot system supplies pilot pressure to the steering and brake system.
- The implement pilot system supplies pilot pressure to the implement system.
Illustration 1 | g06208232 |
Tooling (A) |
Required Tools | ||||
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Tool | Item | Qty | Part Number | Description |
A | 1 | 466-6258 | Communication Adapter Gp | |
A1 | 1 | 457-6114 | Cable As | |
A2 | 1 | - | Current version of Cat ET software | |
A3 | 1 | 370-4617 | Cable As | |
A4 | 1 | 478-0235 | Communication Adapter |
- Move the machine to a smooth, horizontal location that is away from operating machines and away from personnel.
- Place the transmission direction in the NEUTRAL position.
- Engage the parking brake.
- Lower the work tool to the ground.
- Stop the engine.
- Relieve the pressure in the hydraulic system.
Reference: For more information about relieving the hydraulic pressure, refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.
- Install the steering frame lock.
Procedure for Testing the Steering and Brake Pilot System with the Monitor Display
- Navigate the main menu list to display the brake oil pressure on the monitor display..
- Menu>Service>Parameters>Park Brake
- Start and run the engine at low idle rpm. Apply the service brakes and disengage the parking brake. With the oil at normal operating temperature, check pressure (1). Refer to Table 1 for the correct pressure.
- If the pressure reading is correct, engage the parking brake, lower the engine speed, and stop the engine.
- If the pressure reading is not correct, engage the parking brake, lower the engine speed, and stop the engine.
- Proceed with Adjustment Procedure.
- Relieve the pressure in the hydraulic system.
Reference: For more information about relieving the hydraulic pressure, refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.
Illustration 2 | g06267950 |
Check complete.
Illustration 3 | g06267951 |
- Connect the laptop computer to service connector (2) in the cab.
- Start and run the engine at low idle rpm.
- Open the software program (ET). Select the diagnostics tab from the ECM selector menu.
- Select the diagnostics tab.
- Select the "Parking Brake" tab.
Show/hide table
Illustration 4 g06268291 - With the oil at normal operating temperature, check pressure (3). Refer to Table 1 for the correct pressure.
Procedure for Testing the Implement Pilot System with the Caterpillar Electronic Technician (ET)
- Connect the laptop computer to service connector (2) in the cab.
- Start and run the engine at low idle rpm.
- Open the software program (ET). Select the diagnostics tab from the ECM selector menu.
- Select the diagnostics tab.
- Select the implement pilot oil pressure #1 tab.
- With the oil at normal operating temperature, check pressure (5). Refer to Table 1 for the correct pressure.
Illustration 5 | g06267951 |
Illustration 6 | g06254584 |
(4) Accumulator charging valve
(5) Pilot oil pressure reducing valve (implement) (6) Pilot oil pressure reducing valve (steering/brake) |
Accumulator charging valve below the hydraulic tank on the right side of machine
Locate implement pilot pressure reducing valve (5) and steering/brake pressure reducing valve (6) on the underside of brake accumulator charging valve (4) in the service center. Use a hex wrench to loosen the lock-nut and an internal hex wrench to adjust the pilot pressure.
- To increase pressure
- Hold the adjustment screw with the internal hex wrench and loosen the lock-nut
- Turn the adjustment screw inward. A quarter or half turn is often enough to reach the desired setting
- Holding the adjustment screw, tighten the lock-nut
- Recheck the pressure to ensure that the pressure is set as desired
- To decrease pressure
- Hold the adjustment screw with the internal hex wrench and loosen the lock-nut
- Turn the adjustment screw outward first and then, inward to the target pressure. A quarter or half turn is often enough to reach the desired setting
- Holding the adjustment screw, tighten the lock-nut
- Recheck the pressure to ensure that the pressure is set as desired
Note: The last turn of the screw should always be an inward turn, or pressure increase