JLG 120HX Service Manual - Manual (Page 97)

SECTION 3 - TROUBLESHOOTING
3120819 – JLG Lift – 3-11
Motor turns slowly in the direction of the last command.
Valve not returning to neutral. Check neutral springs.
Function speed switch malfunction. Replace function switch.
Sticking spool due to contamination. Remove end cap and check spool freedom.
Repair as necessary.
Motor turns slowly at maximum command.
Valve spool is not traveling far enough due to: Repair or replace drive motor(s).
Worn, leaking drive motor(s). Repair or replace drive motor(s).
Engine RPM’s set too low. Properly adjust engine RPM’s.
Low control pressure supply. Replace pressure regulator if necessary.
Function speed switch malfunction. Replace switch.
Amperage too low on controller. Correctly adjust controller.
Defective pump, low oil volume. Repair or replace pump.
Poor response, function shuts off slowly when command is removed.
Low spool spring preload. Check for correct spring and shims in end caps.
Sticking spool due to contamination. Remove end cap and check spool freedom.
Ramp set too high in controller. Adjust controller.
Sticking control handle. Repair or replace controller.
STEERING SYSTEM.
No response to steer control.
Hydraulic system oil low. Replenish oil as necessary.
Hydraulic system pressure too low. Adjust pressure.
Damaged wiring on control switch or solenoid
valve. See proper wiring diagram.
Control switch not functioning properly. Replace switch.
Restricted or broken hydraulic line on valve
bank, hydraulic pump or rotary coupling. (If
equipped.) Clean, repair or replace line.
If equipped, swivel coupling leaking internally.
(Seals defective.) Repair or replace coupling.
Steer control valve not functioning properly. Repair or replace valve.
Steer cylinder not functioning properly. Repair or replace cylinder.
Table 3-4.Chassis Assembly - Troubleshooting
TROUBLE PROBABLE CAUSE REMEDY