JLG 120HX ANSI Service Manual - Manual (Page 100)

SECTION 3 - TROUBLESHOOTING
3-18 – JLG Lift – 3120686
Pump not delivering oil.
Restricted suction line. Clean, repair, or replace line.
Air entering system through broken line or fitting. Repair or replace line or fitting.
Broken pump drive shaft/pump coupling. Repair or replace pump/pump coupling.
Note: Any time pump or pump drive coupling
is removed coat pump and drive coupling
splines with Lithium Soap Base Grease (TEX-
ACO CODE 1912 OR EQUIVALENT).
Function sluggish during operation. (System
pressure too low.)
Main relief valve set too low. Reset valve as required.
Pump section not delivering sufficient oil. Repair or replace pump section or pump.
Main relief valve stuck in open position. Clean, repair, or replace valve. (Check system oil
for contamination.)
Oil viscosity too low. Drain system and replace with recommended oil.
(Refer to Hydraulic Oils.)
Leak in component, line or fitting. Repair or replace component, line or fitting.
Scored valve spool; scored cylinder. Replace valve; replace cylinder.
Amperage too low on controller. Correctly adjust controller.
Low sequence pressure. Reset valve as required.
Low pilot pressure. Reset valve as required.
Wrong/defective spool in drive section. Repair or replace drive section.
Shuttle balls leaking in proportional valve. Repair or replace valve.
Low voltage in electrical system. Correct low voltage problem.
System(s) operate erratically.
Sticking or binding valve spools, pistons. Clean, repair, or replace components as
required.
AUXILIARY HYDRAULIC SYSTEM.
Auxiliary hydraulic pump inoperable.
Circuit breaker open. Determine and correct cause; reset circuit
breaker.
Engine is running. Shut down engine.
Check valve in system leaking. Repair or replace check valve.
Battery requires charging or will not hold a
charge. Charge or replace battery as required.
Table 3-5.Hydraulic System - Troubleshooting
TROUBLE PROBABLE CAUSE REMEDY