Hyundai HL955 Manual page 140

Problem
Transmission pressure is
low (all gears)
Tr a n s m i s s i o n s y s t e m
pressure is low (one or
two gears)
Transmission shifts too
low
Cause
Low oil level.
Failed transmission pressure
switch.
Plugged suction strainer.
Stuck transmission pressure
regulating valve or broken spring.
Failed control valve gasket.
Stuck PPC valve.
Failed transmission pump.
Failed transmission control valve
gasket.
Leakage in clutch piston or seal
ring.
Low oil level (aeration of oil).
Low transmission pressure.
Restricted transmission pump
suction screen.
Low transmission pump flow.
Excessive transmission
element leakage.
Stuck PPC valve.
Restricted PPC valve orifice.
Restricted oil passages between
control valve and transmission
elements.
Incorrect transmission oil.
3-84
Remedy
Check transmission oil level and refill if
necessary.
Verify transmission system pressure. Do
transmission system pressure test.
Transmission pump may be noisy if transmission
suction screen is clogged. Drain transmission.
Remove and clean suction screen.
Also, check condition of transmission filter.
Remove transmission pressure regulating valve.
Inspect for damage (See transmission control
valve).
Inspect transmission control valve for external
leakage. Remove control valve.
Inspect or replace gasket.
Remove end cover to inspect modulation spool
and check torque on cap screws retaining
control valve to transmission.
Do pump flow test.
Inspect transmission control valve for external
leakage. Remove control valve.
Inspect or replace gasket.
Disassemble and repair.
Add oil.
Do transmission system pressure test.
Remove and clean screen.
Do transmission pump flow test.
Do transmission element leakage test using
system pressure.
Remove end cover to inspect modulation spool.
Replace if necessary.
Remove orifice and inspect for contamination
and /or plugging.
Remove control valve and inspect oil passage.
Change oil (SAE 10W-30/15W-40)