Troubleshooting Boom Lowering Failure on the JLG 45HAE

[MikePhua]

The JLG 45HAE and Its Historical Footprint
The JLG 45HAE articulating boom lift was introduced in the early 1990s as part of JLG Industries’ push to expand its electric-powered aerial work platform lineup. JLG, founded in 1969 in Pennsylvania, quickly became a global leader in access equipment, with its boom lifts widely adopted in construction, maintenance, and industrial sectors. The 45HAE offered a 45-foot platform height, horizontal outreach of over 20 feet, and an articulating jib for precision positioning. Its electric drive system made it ideal for indoor and noise-sensitive environments. Thousands of units were sold across North America and Europe, and many remain in service today due to their robust design and modular component architecture.
Symptoms of Boom Lowering Failure
A recurring issue with aging 45HAE units involves the boom refusing to lower beyond a horizontal position. In one documented case, the boom had been stored horizontally for several months and would not descend further, even after replacing the control valve and inspecting internal orifices. The only temporary solution was manually bleeding hydraulic pressure from the cylinder, which allowed the boom to lower—but the problem returned upon reactivation.
This behavior suggests a mechanical or hydraulic lockout condition, possibly related to cylinder internals, valve sequencing, or safety interlocks.
Terminology Notes

• Control valve: A hydraulic component that regulates fluid flow to actuators based on operator input.
  
• Orifice: A calibrated opening in a hydraulic circuit that controls flow rate and pressure.
  
• Hydraulic cylinder: A linear actuator powered by pressurized fluid to extend or retract mechanical arms.
  
• Bleeding pressure: Releasing trapped hydraulic fluid to relieve internal pressure and allow movement.
  

Root Cause Analysis and Diagnostic Strategy
The most likely causes of this issue include:

• Cylinder bypass or internal scoring: If the piston seal is damaged, fluid may not flow properly during retraction.
  
• Check valve malfunction: A stuck or failed check valve can prevent fluid from returning to the reservoir.
  
• Boom angle sensor fault: Some models include angle sensors that prevent lowering beyond safe limits.
  
• Safety interlock override failure: The system may interpret the boom position as unsafe and block further descent.
  

To diagnose:

1. Inspect the hydraulic cylinder for signs of scoring or seal damage.
   
2. Test the control valve under load to verify actuation and return flow.
   
3. Check for electrical interlocks or angle sensors that may be misreading boom position.
   
4. Use a manual override or auxiliary hydraulic source to test cylinder response independently.
   

In one case from Ontario, a technician discovered that the boom’s descent was blocked due to a misaligned limit switch that falsely indicated full retraction. Realigning the switch restored normal operation.
Field Anecdotes and Lessons Learned
A maintenance crew in Arizona reported similar symptoms on a 1993 JLG 45HAE. After replacing the valve and inspecting the cylinder, they found that the boom’s hydraulic lines had developed internal delamination, restricting fluid flow. Replacing the hoses resolved the issue.
In another case from Sweden, a rental firm had stored a 45HAE outdoors for six months. Moisture had entered the valve body, causing corrosion and partial blockage. After ultrasonic cleaning and seal replacement, the boom resumed full range motion.
Preventive Measures and Recommendations
To avoid boom lowering failures:

• Store the lift with the boom slightly elevated to prevent seal compression.
  
• Cycle the boom monthly to maintain fluid movement and prevent valve sticking.
  
• Replace hydraulic fluid every 1,000 hours or annually to prevent contamination.
  
• Inspect and clean valve bodies during every major service.
  
• Use dielectric grease on electrical connectors to prevent sensor misreads.
  

Final Thoughts
The JLG 45HAE remains a reliable platform when maintained properly, but its hydraulic and control systems can develop quirks with age and storage conditions. When the boom refuses to lower, the issue is often deeper than the valve—requiring a full-system inspection from cylinder to sensor. With careful diagnostics and preventive care, these machines can continue serving safely and efficiently for decades. In aerial work platforms, movement is everything—and when it stops, the solution lies in understanding the system as a whole.