JLG 150HAX ANSI Service Manual - Manual (Page 140)

SECTION 6 - SCHEMATICS
6-12 – JLG Lift – 3120679
Machine will not travel in forward.
Hydraulic system oil low. Replenish oil as necessary.
Restricted or broken hydraulic line or
fitting. Clean, repair or replace line or fitting.
Control valve not functioning properly. Repair or replace valve.
Drive motor(s) not functioning properly. Repair or replace motor(s).
Circuit breaker open. Determine and correct cause; reset
circuit breaker.
Counterbalance valve sticking on
return side. Adjust return counterbalance out 3 turns - cycle
drive - return to original
position.
Machine will not travel in reverse.
See: Machine will not travel in forward.
Machine overspeeds when descending a grade.
Counterbalance valve improperly
adjusted or defective. Adjust or replace valve.
Motor turns slowly in the direction of the last command.
Failed controller resulting in a
command at neutral position. Replace controller.
Failed pilot valve. Replace pilot valve.
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:
Low pressure gain of pilot valve. Check filter in the inlet section for restriction.
Low control pressure supply. Replace pressure regulator if necessary.
Plugged pilot valve. Change pilot valve.
Table 6-4.Chassis - Troubleshooting
TROUBLE PROBABLE CAUSE REMEDY