Hyundai HL955 Manual page 513

Problem
No steering or hydraulic
function
No hydraulic functions
steering normal
Boom float function
does not work
One hydraulic function
does not work.
Low hydraulic power
Cause
Low oil level.
Failed hydraulic pump.
Failed hydraulic pump.
Failed line filter.
Faulty safety valve.
Stuck open port relief valve.
Low pilot control pressure.
Faulty pilot control valve (RCV).
Loader control valve (MCV) spool
binding in bore.
Faulty pilot control valve (RCV).
Stuck open port relief valve.
Oil leaking past cylinder packings.
Blockage in oil lines or valve.
Loader control valve (MCV) spool stuck
in bore.
Leakage within work circuit.
Low system relief valve (main relief
valve) setting.
Low port relief valve setting.
Leaking system relief valve.
Worn hydraulic pump.
Faulty pilot control valve (RCV).
6-48
Remedy
Add recommended oil.
Remove and inspect return filter for
metal pump particles.
Remove and inspect return filter for
metal pump particles, or replace the
pump.
Remove and inspect line filter for RCV.
Safety valve leakage test or ON, OFF
function test.
Replace relief valve.
Do pressure reducing valve pressure
test in group 3.
Replace relief valve.
Do pressure reducing valve pressure
test in group 3.
Do pilot control valve pressure test.
Inspect and repair valve.
Replace relief valve.
Do boom and bucket cylinder leakage
test in group 3.
Inspect lines for damage.
Disconnect and inspect lines for internal
blockage.
Inspect and repair valve.
Do cylinder drift check in group 2.
Do loader system and port relief valve
pressure test in group 3.
Do loader system and port relief valve
pressure test in group 3.
Remove and inspect valve.
Do hydraulic pump performance check
in group 2.
Do pilot control valve pressure test in
group 3.