SkyTrak 8042 Telehandler Troubleshooting Hydraulic and Electrical Faults

[MikePhua]

The SkyTrak 8042 and Its Place in Material Handling
The SkyTrak 8042 is a rough terrain telehandler designed for lifting and placing materials in construction, agriculture, and industrial logistics. Manufactured by JLG Industries, a company founded in 1969 and now a global leader in aerial work platforms and telehandlers, the 8042 model offers an 8,000-pound lift capacity and a maximum reach of 42 feet. Its four-wheel drive, frame leveling, and boom-mounted joystick controls make it a versatile choice for uneven terrain and tight job sites.
With thousands of units sold across North America and beyond, the 8042 has become a staple in rental fleets and contractor yards. Its mechanical simplicity and robust hydraulic system are praised by operators, but like any machine, it can develop faults—especially in older units or those exposed to harsh conditions.
Terminology Annotation

• Telehandler: A telescopic handler used to lift and place loads at height or distance, often equipped with forks or buckets.
  
• Boom Function: The hydraulic movement of the telescoping arm, including lift, extend, and tilt.
  
• Solenoid Valve: An electrically actuated valve that directs hydraulic flow to specific functions.
  
• Joystick Controller: The operator’s interface for controlling boom and auxiliary functions, often linked to proportional valves.
  

Common Symptoms and Diagnostic Pathways
Operators may encounter issues such as:

• Boom functions failing intermittently or completely
  
• Hydraulic movement limited to one direction (e.g., up but not down)
  
• Joystick unresponsive or erratic
  
• Audible solenoid clicks without hydraulic response
  
• Engine running normally but no boom movement
  

These symptoms often point to faults in the electrical control system, solenoid valves, or hydraulic flow path. In one documented case, a SkyTrak 8042 lost all boom functions except for lift. The joystick would engage the solenoid, but no movement occurred. After tracing the wiring, a broken ground connection was found near the frame rail—corroded and hidden beneath a bracket.
Electrical System and Solenoid Behavior
The 8042 uses a series of solenoids mounted on the hydraulic valve block to control boom functions. Each solenoid is activated by the joystick, sending current through a relay and energizing the valve. If the solenoid receives voltage but does not actuate, the issue may be:

• Internal coil failure
  
• Stuck spool due to contamination
  
• Broken wire or poor ground
  
• Faulty relay or joystick output
  

Recommended steps:

• Use a multimeter to check voltage at the solenoid during joystick actuation
  
• Listen for a click indicating coil engagement
  
• Test continuity from joystick to solenoid
  
• Inspect ground wires for corrosion or loose connections
  
• Swap solenoids to isolate the fault
  

In one repair, a technician bypassed the joystick and manually energized the solenoid using a jumper wire. The boom extended normally, confirming the hydraulic system was functional and the fault was electrical.
Hydraulic Flow and Contamination Risks
If solenoids are functioning but movement is still restricted, the issue may lie in the hydraulic circuit:

• Clogged filters or screens
  
• Air in the lines causing cavitation
  
• Low fluid level or degraded fluid
  
• Worn pump or relief valve malfunction
  

Solutions include:

• Checking fluid level and condition
  
• Replacing hydraulic filters
  
• Bleeding the system to remove air
  
• Testing pump pressure with a gauge
  
• Inspecting valve spools for debris or scoring
  

In one fleet, a SkyTrak unit showed sluggish boom movement. Fluid analysis revealed water contamination from a cracked reservoir cap. After flushing the system and replacing the cap, performance returned to normal.
Joystick and Control Logic Issues
The joystick itself can fail due to:

• Worn potentiometers or switches
  
• Broken internal springs
  
• Connector corrosion
  
• Misalignment of mechanical linkages
  

To diagnose:

• Remove joystick cover and inspect internal components
  
• Test output voltage or resistance during movement
  
• Clean connectors with contact cleaner
  
• Replace joystick if mechanical damage is found
  

Some operators retrofit newer joystick assemblies with sealed electronics to improve reliability in wet or dusty environments.
Preventative Measures and Upgrade Suggestions
To reduce future faults:

• Install sealed connectors and dielectric grease on all terminals
  
• Add a ground bus bar for centralized grounding
  
• Use weatherproof solenoids with molded coils
  
• Replace hydraulic fluid annually or every 1,000 hours
  
• Label all wires and solenoids for easier troubleshooting
  

In one rental fleet, adding LED indicators to each solenoid circuit allowed technicians to visually confirm activation, reducing diagnostic time by 50%.
Conclusion
The SkyTrak 8042 telehandler is a durable and capable machine, but its boom functions depend on a clean hydraulic system and reliable electrical control. When faults arise, methodical diagnosis—starting with solenoids and grounding—can restore performance quickly. With preventative upgrades and careful inspection, operators can keep the 8042 lifting reliably across seasons and job sites. In the world of rough terrain handling, clarity in wiring and cleanliness in hydraulics are the keys to uptime.