JLG 20VP (3120849) Service Manual - Manual (Page 91)

SECTION 3 - TROUBLESHOOTING
3120849 – JLG Lift – 3-35
Platform (Mast) Won’t Stay Elevated
Overview Of Procedure
The following procedure requests that the lift down, dump, and pump internal valves be checked to see if any are stuck
open, it also examines the lift down and dump valve circuits. Also suggests that the lift cylinder packing could be leaking
internally.
Check For These Obvious Conditions First:
• Manual descent valve is closed tight.
Table 3-29. Platform (Mast) Won’t Stay Elevated.
STEP ACTION SPEC YES NO
1. Is the lift down valve stuck open?
—
Repair or Clean
Valve
Go to Step 2
2. Check the valve inside the pump, it could be stuck open. — Replace Pump Go to Step 3
3. Lift down valves could be open due to incorrect electrical signal.
—
Check Pump
Valve Electrical
Circuit
(Table 3-22)
Go to Step 4
4. Dump valve could be open due to incorrect electrical signal.
—
Check Pump
Valve Electrical
Circuit
(Table 3-22)
Go to Step 5
5. Oil could be passing around the lift cylinder bore packing.
—
Replace or
Rebuild the Lift
Cylinder
—