2007 JLG 400S Boom Lift Slow Response and Failure Overview

[MikePhua]

The 2007 JLG 400S is a telescopic boom lift designed for aerial work requiring a maximum platform height of approximately 40 feet. It features a robust diesel engine and a four-wheel drive system, making it suitable for a variety of rough terrain construction and maintenance tasks.
Specifications

• Maximum platform height: 40 feet
  
• Working height: roughly 46 feet (including operator height)
  
• Horizontal outreach: around 33 feet
  
• Lift capacity: 500 lbs
  
• Engine: Diesel, typically a Deutz or similar 49-50 hp engine
  
• Weight: Approximately 12,500 to 13,600 pounds (5,670 - 6,180 kg)
  
• Platform size: 96 inches wide by 36 inches deep
  
• Gradeability: 45%
  
• Drive system: 4WD for rough terrain capability
  
• Boom rotation: Full 360 degrees
  

Typical Issues with Slow Boom Lift Response and Failures
Owners of the 2007 JLG 400S have reported issues of slow response in boom lift function and eventual failure to operate lift controls smoothly or at all. These problems often arise due to:

• Hydraulic system failures: Contaminated or low hydraulic fluid, worn seals or valves, or pump degradation can cause sluggish boom response.
  
• Control valve malfunctions: Sticky or worn control valves may impair fluid flow critical for precise boom extension and retraction.
  
• Electrical or sensor faults: Faulty joystick controls, wiring harness damage, or sensor failures can disrupt signal transmission.
  
• Load sensor or pressure switch failures: If safety sensors detect overload or pressure abnormalities, the system may throttle or disable lift functions to prevent damage.
  
• Fuel or engine issues: Lack of engine power due to fuel system clogs or engine wear can indirectly affect hydraulic pump output.
  

Troubleshooting and Solutions

• Check hydraulic oil level, cleanliness, and quality; replace or flush if contaminated.
  
• Inspect hydraulic hoses, fittings, and cylinders for leaks and repair as needed.
  
• Test pump pressures and flow rates using service tools to determine hydraulic pump health.
  
• Examine control valves for wear or blockage; clean or replace faulty units.
  
• Verify electrical system integrity including joysticks, wiring, and sensors.
  
• Use factory diagnostic tools, such as JLG’s service software, to scan error codes.
  
• Replace or repair failed sensors and switches that control safety interlocks.
  
• Maintain regular service intervals, replacing filters and fluids.
  
• If persistent, consider professional hydraulic system overhaul.
  

Terminology

• Hydraulic Pump: Converts engine power into hydraulic pressure to move the boom and platform.
  
• Control Valve: Directs hydraulic fluid to specific actuators to move the boom.
  
• Gradeability: The maximum slope the lift can safely ascend or descend, expressed in percent.
  
• Load Sensor: Detects the weight being lifted to regulate operation for safety.
  
• Joystick Control: Operator interface for boom positioning and movement.
  

A Small Story
A maintenance crew operating a 2007 JLG 400S on a construction site found the boom lift sluggish during extension and unresponsive at times. After routine inspection, hydraulic fluid was found dirty and at low levels due to a slow leak in a hose. After replacing the hose and fluid, the response improved, though further inspection revealed a worn control valve requiring replacement to restore full functionality. The story underscores the importance of routine hydraulic and electrical maintenance for performance and safety.
Summary List

• 2007 JLG 400S key specs: 40 ft platform height, 500 lb capacity, diesel engine, 4WD.
  
• Slow boom response often linked to hydraulic fluid issues, control valves, or sensors.
  
• Troubleshooting includes hydraulic fluid check, pump and valve testing, electrical diagnostics.
  
• Safety sensors regulate lift operation; failures can cause functionality loss.
  
• Regular maintenance critical to prevent response degradation.
  
• Professional diagnostics recommended for persistent or complex faults.
  

Careful inspection and maintenance of hydraulic and electrical components ensure reliable operation of the JLG 400S boom lift, minimizing downtime and optimizing safety on job sites.