JLG 40H Service Manual - Manual (Page 123)

SECTION 3 - TROUBLESHOOTING
3120240 – JLG Lift –
3-11
TROUBLE PROBABLE CAUSE REMEDY
Machine will not travel in forward. Hydraulic system oil low.
Restricted or broken hydraulic line or fitting.
Control valve not functioning properly.
Drive motor(s) not functioning properly.
Circuit breaker open.
No power to wheel motor speed switch.
Two speed valve sticking.
Counterbalance valve sticking on return side.
Replenish oil as necessary.
Clean, repair or replace line or fitting.
Repair or replace valve.
Repair or replace motor(s).
Determine and correct cause; reset circuit breaker.
See proper wiring diagram.
Repair or replace valve.
Adjust return counterbalance out 3 turns - cycle
drive - return to original position.
Machine over speeds when descending a grade. Counterbalance valve improperly adjusted or
defective.
Adjust or replace valve.
Motor turns slowly in the direction of the last
command. Valve not returning to neutral.
Function speed switch malfunction.
Sticking spool due to contamination.
Check neutral springs.
Replace function switch.
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:
Worn, leaking drive motor(s).
Engine speed too low.
Low control pressure supply.
Function speed switch malfunction.
Amperage too low on controller.
Defective pump, low oil volume.
Repair or replace drive motor(s).
Properly adjust engine speed.
Replace pressure regulator if necessary.
Replace switch.
Correctly adjust controller.
Repair or replace pump.
Poor response, function shuts off slowly when
command is removed. Low spool spring preload.
Sticking spool due to contamination.
Ramp set too high in controller.
Sticking control handle.
Check for correct spring and shims in end cap.
Remove end cap and check spool freedom.
Adjust controller.
Repair or replace controller.