Why Won’t My Skyjack Scissor Lift Move or Go Up

[MikePhua]

The Rise of Skyjack and Its Scissor Lift Legacy
Skyjack, founded in 1985 in Ontario, Canada, quickly became a dominant force in the aerial work platform industry. Known for its rugged design and intuitive controls, Skyjack scissor lifts are widely used in construction, warehousing, and facility maintenance. By the early 2000s, Skyjack had sold hundreds of thousands of units globally, with the SJIII series becoming a staple on job sites due to its reliability and ease of service.
Scissor lifts like the SJIII 3219 and SJIII 4632 are designed to provide vertical access with minimal footprint. Their electric models are favored for indoor use, offering quiet operation and zero emissions. Despite their robust engineering, these machines can experience operational failures—particularly when they refuse to lift or drive.
Initial Checks Before Troubleshooting
Before diving into diagnostics, operators should perform a safety sweep:

• Ensure the emergency stop button is disengaged
  
• Confirm the platform control selector is in the correct position
  
• Check that the lift is on level ground and not in tilt alarm mode
  
• Verify that the battery disconnect switch is turned on
  

These simple steps resolve many non-start issues. A technician in Texas once spent hours tracing wiring faults only to discover the emergency stop was engaged—a reminder that basic checks matter.
Power Supply and Battery Health
The most common cause of lift failure is insufficient power. Skyjack scissor lifts rely on deep-cycle batteries, typically four 6V units wired in series to deliver 24V. If voltage drops below 21V under load, the lift may refuse to operate.
Battery terminals should be clean and tight. Corrosion increases resistance, reducing available current. A multimeter test under load can reveal weak cells. If one battery reads significantly lower than the others, it should be replaced. Equalizing charge cycles every 30 days helps maintain battery health.
A warehouse in Ohio reported frequent lift failures during winter. The culprit was cold battery performance—capacity drops by up to 50% at freezing temperatures. Installing battery warmers and switching to AGM batteries improved reliability.
Hydraulic System and Lift Function
The hydraulic system powers the lifting mechanism. If the lift won’t rise, check the following:

• Hydraulic fluid level: should be within the sight gauge range
  
• Lift cylinder holding valves: may be stuck closed or manually overridden
  
• Hydraulic pump motor: should engage audibly when the lift button is pressed
  

Air in the hydraulic lines can cause erratic movement. Bleeding the system restores smooth operation. A technician in Florida discovered a slow lift was due to a partially clogged return filter, which restricted flow and caused backpressure.
Hydraulic leaks are another concern. Inspect hoses for cracks, especially near fittings and bends. Replace any damaged lines immediately. Use ISO 32 hydraulic oil unless otherwise specified.
Drive System and Mobility Issues
If the lift powers on but won’t drive, the issue may lie in the drive solenoids or joystick controller. Common causes include:

• Faulty drive solenoid coils: test resistance with an ohmmeter
  
• Damaged wiring harness: look for pinched or frayed wires
  
• Stuck drive valve: may need cleaning or replacement
  

Skyjack drive motors are typically DC units with planetary gear reduction. If the lift moves slowly or not at all, inspect motor brushes and commutators. A technician in Alberta resolved a no-drive issue by replacing a worn joystick potentiometer, which was sending erratic signals to the controller.
Control Panel and Sensor Feedback
Modern Skyjack lifts use a control logic system that monitors sensor inputs. If any sensor reports an unsafe condition, the lift will lock out movement. Key sensors include:

• Tilt sensor: disables lift if angle exceeds safe threshold
  
• Platform load sensor: prevents lift if overloaded
  
• Limit switches: detect full extension or retraction
  

A common failure involves the tilt sensor triggering falsely due to vibration or loose mounting. Recalibrating or replacing the sensor restores function. Always check diagnostic LEDs on the control panel for fault codes.
Reset Procedures and Software Checks
Sometimes, a full system reset is required. To perform a reset:

• Turn off the lift
  
• Disconnect the battery for 60 seconds
  
• Reconnect and power on
  

This clears temporary faults in the controller. If issues persist, software updates may be needed. Skyjack controllers can be reprogrammed via diagnostic tools, though this requires manufacturer support.
Terminology Notes

• Solenoid Valve: An electrically controlled valve that directs hydraulic flow
  
• Potentiometer: A variable resistor used to measure joystick position
  
• Planetary Gear: A gear system that multiplies torque in compact form
  
• ECU (Electronic Control Unit): The onboard computer managing lift functions
  
• Bleeding: The process of removing air from hydraulic lines
  

Preventive Maintenance Recommendations
To avoid lift failures, implement a regular maintenance schedule:

• Battery inspection and cleaning: weekly
  
• Hydraulic fluid check: monthly
  
• Electrical connector inspection: quarterly
  
• Sensor calibration: annually
  
• Full system diagnostic: every 500 hours
  

Use dielectric grease on connectors to prevent corrosion. Label wires during repairs to simplify future troubleshooting.
Conclusion
Skyjack scissor lifts are engineered for reliability, but like all machines, they require attentive care. When a lift refuses to move or rise, the solution often lies in power supply, hydraulic integrity, or control logic. By understanding the interplay of these systems and applying structured diagnostics, operators can restore function quickly and safely. With proper maintenance, a Skyjack lift can serve faithfully for over a decade, elevating productivity across industries.