SECTION 3 - TROUBLESHOOTING
3120686
– JLG Lift –
3-3
.
Table 3-2.Boom Assembly - Troubleshooting
TROUBLE
PROBABLE CAUSE
REMEDY
CONTROL VALVE
S
Valve spool sticking.
Dirt in oil causing excessive temperature build-
up.
Flush system and change oil using recom-
mended viscosity
Moisture in oil.
Flush system and change oil using recom-
mended viscosity
Incorrect valve mounting causing warping of the
unit.
Loosen valve and check mounting. Repair as
necessary.
Valve spool scored.
Remove valve and repair or replace as neces-
sary.
Tie-bolts in valve over torqued.
Correctly torque bolts.
Return spring weak or broken.
Remove valve and repair or replace as neces-
sary.
Relief valve malfunctioning causing excessive
pressure within valve.
Check pressure delivery to and from valve and
repair or replace as necessary.
Valve leaking.
Dirt or other foreign material under seal.
Remove and repair valve as necessary.
Valve spool scored.
Remove valve and repair or replace as neces-
sary.
Excessive back pressure caused by restricted
return line to reservoir.
Remove line and clear obstruction or replace line
as necessary.
Damaged valve seals.
Remove valve and repair or replace as neces-
sary.
BOOM ELEVATION SYSTEM.
No response to lift control switch.
Lift function not activated within 7 seconds after
footswitch was depressed.
Recycle footswitch.
Lift control switch inoperative.
Repair or replace control switch.
Lift cylinder holding valve inoperative.
Repair or replace holding valve.
Dump valve (bypass) not operating.
Determine cause and repair or replace valve.
Electrical malfunction.
See wiring diagram.
Hydraulic system oil low.
Replenish oil as necessary.
Restricted or broken supply line on valve bank or
hydraulic pump.
Clean or replace line.
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