JLG 40H Service Manual - Manual (Page 117)

SECTION 3 - TROUBLESHOOTING
3120240 – JLG Lift –
3-5
Boom will not extend. Control valve not functioning properly.
Damaged wiring on control switch or solenoid valve.
Restricted or broken supply line on fitting.
Pressure setting incorrect.
Telescope cylinder not functioning properly.
Repair or replace control valve.
Repair or replace wiring.
Clean, repair, or replace line or fitting.
Check pressure/readjust as necessary.
Repair or replace cylinder.
Boom extends and retracts erratically. Hydraulic system oil low.
Wear pads worn.
Restricted or broken supply line on fitting.
Control valve not functioning properly.
Worn seal(s) in telescope cylinder.
Cylinder not functioning properly.
Distorted boom section (s).
Counterbalance valve not functioning properly.
Replenish oil as necessary.
Replace pads as required.
Clean, repair, or replace line or fitting.
Repair or replace valve.
Replace seal(s).
Repair or replace cylinder.
Replace distorted section (s).
Replace counterbalance valve.
BOOM SWING SYSTEM.
No response to control. Hydraulic system oil low.
Swing control lever not functioning.
Restricted or broken supply line on valve bank or
hydraulic pump.
Control valve not functioning properly.
Swing motor not functioning properly.
Swing brake not releasing.
Restrictor valve(s) plugged.
Foreign objects wedged between swing motor pin-
ion and swing gear.
Sheared shaft on swing motor/brake.
Pressure reducing valve in swing circuit malfunc-
tioning.
No electric power to valve.
Replenish oil as necessary.
Repair or replace swing control lever.
Clean or replace line.
Repair or replace valve.
Repair or replace motor.
Repair or replace brake.
Clean or replace restrictor valve.
Remove objects, check for damage, and repair or
replace component (s) as required.
Repair or replace motor/brake.
Repair or replace pressure reducing valve.
See proper wiring diagram.
TROUBLE PROBABLE CAUSE REMEDY