JLG Scissor Lift Works but Won’t Go Down: Troubleshooting and Solutions

[MikePhua]

JLG scissor lifts are widely used in various industries for lifting personnel and equipment to elevated heights. However, like any heavy machinery, they can experience issues from time to time. One common problem that users encounter is when the scissor lift operates normally to go up but won’t lower as expected. This can be a frustrating issue, but understanding the possible causes and solutions can help you resolve it quickly.
Symptoms of the Problem
When facing this issue, operators may notice the following symptoms:

1. The Lift Moves Up Normally: The scissor lift will go up without any issues, indicating that the power and hydraulics are functioning to some extent.
   
2. Lift Will Not Lower: Despite normal upward movement, the lift will fail to descend when the control is engaged, even after waiting a few moments.
   

Common Causes of the Issue
Several potential factors can contribute to this problem, including hydraulic and control system issues. Below are some of the most common causes:

1. Hydraulic Fluid Issues:
   • If the hydraulic fluid is low or contaminated, the lift may fail to descend. Hydraulic fluid plays a crucial role in controlling the movement of the lift, and without adequate or clean fluid, the lift may struggle to respond to the lowering command.
     
2. Faulty Solenoid Valve:
   • A malfunctioning solenoid valve may prevent the hydraulic fluid from flowing correctly through the system, especially to the lowering circuit. The solenoid valve controls the release of hydraulic fluid to lower the lift. If it is stuck or broken, the lift may not descend.
     
3. Blocked or Stuck Hydraulic Valve:
   • A hydraulic valve that is blocked, damaged, or improperly functioning can restrict the flow of fluid needed to lower the lift. This could be due to debris or internal wear within the valve.
     
4. Control Valve Malfunction:
   • The control valve, which directs hydraulic fluid to the appropriate circuits, might be malfunctioning. If the control valve isn’t working correctly, it could prevent the lift from responding to the lowering command.
     
5. Electrical Issues:
   • Electrical components, such as the control circuit, can sometimes cause problems with hydraulic system activation. A loose or corroded wire in the control circuit may result in a failure to engage the lowering function.
     
6. Pressure Relief Valve Issue:
   • The pressure relief valve prevents the hydraulic system from exceeding a set pressure. If this valve is damaged or malfunctioning, it can restrict the ability to lower the lift, as it will not release the pressure appropriately.
     

Troubleshooting the Issue
To resolve the issue of the JLG scissor lift not lowering, follow these troubleshooting steps:

1. Check Hydraulic Fluid:
   • Start by checking the hydraulic fluid level. Ensure that it is at the appropriate level and that the fluid is clean and free of contaminants. Low or dirty fluid can cause performance issues in the hydraulic system. If necessary, top up or replace the fluid and inspect the system for leaks.
     
2. Inspect the Solenoid Valve:
   • Test the solenoid valve for proper operation. If the valve is stuck or malfunctioning, it may prevent the hydraulic fluid from circulating in the lowering circuit. Check for any electrical issues or signs of wear, and if necessary, replace the solenoid valve.
     
3. Examine the Hydraulic Valves:
   • Inspect the hydraulic valves for blockages or damage. Clean or replace any valves that appear to be blocked or worn out. Also, check for any signs of leakage, which could indicate internal damage.
     
4. Test the Control Valve:
   • Ensure that the control valve is functioning properly. If the valve isn’t directing fluid to the right circuits, the lift will not lower. Consider replacing the control valve if it seems to be malfunctioning.
     
5. Inspect the Pressure Relief Valve:
   • Check the pressure relief valve to ensure it is not stuck or damaged. If the valve is malfunctioning, it could prevent the hydraulic system from releasing pressure and lowering the lift. Replace any faulty components.
     
6. Check Electrical Wiring and Connections:
   • Inspect the electrical wiring and connections, especially those linked to the lowering function. Ensure that all wires are securely connected and free of corrosion. Any damaged or corroded connections should be cleaned or replaced.
     
7. Test the Batteries and Control Circuit:
   • If electrical problems persist, check the battery voltage and the control circuit for faults. A weak battery or a malfunctioning control circuit could affect the performance of the lift.
     

Preventive Maintenance
To avoid future problems with the lowering function of your JLG scissor lift, consider the following preventive maintenance practices:

1. Regularly Check Hydraulic Fluid Levels:
   • Check the hydraulic fluid regularly to ensure it remains clean and at the correct level. Contaminants can cause internal damage, so it is important to replace the fluid when necessary.
     
2. Inspect Valves Periodically:
   • Periodically check the solenoid and hydraulic valves for wear, blockages, or malfunctions. Regular maintenance can prevent the need for major repairs.
     
3. Clean Electrical Connections:
   • Ensure all electrical connections, particularly those related to the control system, are free of corrosion and wear. This will improve the responsiveness and reliability of the scissor lift.
     
4. Test the Pressure Relief Valve:
   • Check the pressure relief valve to ensure it is functioning properly and can safely release hydraulic pressure when needed.
     

Conclusion
When a JLG scissor lift works but won’t lower, the problem often lies within the hydraulic system, solenoid valve, control valve, or electrical components. By following a systematic troubleshooting approach and addressing common issues such as low hydraulic fluid, faulty valves, and electrical malfunctions, you can restore the lift's ability to function properly. Regular preventive maintenance is essential to ensure the longevity and proper operation of the scissor lift, minimizing the risk of future breakdowns.