JLG 450A Service And Maintenance Manual page 88

SECTION 3 - TROUBLESHOOTING
TROUBLE
Boom will not raise.
Boom will not lower.
Boom raises and lowers erratically.
Boom drifts down.
3-4
Table 3-2.Boom Assembly - Troubleshooting
PROBABLE CAUSE
Control valve not functioning properly.
Lift cylinder not functioning properly.
Lift function not activated within 7 seconds after
footswitch was depressed.
Load capacity exceeded (personnel or equip-
ment on platform).
Hydraulic system oil low.
Electrical failure to valves.
Restricted or broken hydraulic line or fitting.
Control valve not functioning properly.
Pressure relief valve not functioning properly.
Bypass valve (dump) not functioning.
Lift cylinder not functioning properly.
Binding lift cylinder or boom pivot pin.
See: Boom will not raise.
Pressure relief valve not functioning properly.
Holding valve not functioning properly.
Hydraulic system oil low.
Restricted or broken hydraulic line or fitting.
Counterbalance valve on lift cylinder improperly
adjusted or not functioning properly.
Control valve not functioning properly.
Worn seals in lift cylinder.
Cylinder not functioning properly.
Worn seals in lift cylinder.
– JLG Lift –
REMEDY
Repair or replace valve.
Repair or replace cylinder
Recycle footswitch.
Reduce load.(Refer to capacity placard.)
Replenish oil as necessary.
See proper wiring diagram.
Clean, repair, or replace line or fitting.
Repair or replace valve.
Re-adjust or replace valve.
Repair or replace valve.
Repair or replace cylinder.
Repair or replace cylinder or pin.
Re-adjust or replace valve.
Re-adjust or replace valve.
Replenish oil as required.
Clean, repair, or replace line or fitting.
Replace valve.
Repair or replace valve.
Replace seals.
Repair or replace cylinder.
Replace seals.
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