Hitachi ZAXIS 135US-6 class Operator's Manual page 474

Hydraulic System
When the machine is stored without operation, air mixed in hydraulic oil will become separated and will accumulate
in the cylinder upper sections, causing a delay in the response time of the machine movement or weak power
development.
In case these symptoms appear, repeatedly operate all actuators several times.
Problem
No hydraulic Functions
(Noise from pumps)
No hydraulic Functions
(Hydraulic pump noise remains
unchanged.)
All actuators have no power.
Only one side lever is inoperable or has
no power.
TROUBLESHOOTING
Cause
Faulty hydraulic pump
Lack of hydraulic oil
Broken suction pipe and/or hose
Faulty pilot pump
Faulty pilot shut-off solenoid valve
Faulty wire harness (pilot shut-off solenoid
valve) pilot shut-off switch.
The pilot control shut-off lever is in the LOCK
position.
Malfunction due to worn hydraulic pump
Decreased main relief valve set pressure in the
control valve
Lack of hydraulic oil
Clogged suction strainer in the hydraulic oil
tank
Absorption of air from the oil suction side
Faulty pressure sensor.
Faulty solenoid valve
Faulty relief valve in the valve
Broken pipe and/or hose
Loose pipe line joint
Broken O-ring at pipe line joint
Faulty hydraulic pump
Faulty pilot valve
Faulty pilot circuit line
Faulty pilot solenoid valve
11-4
* Repair or replace
Refill
* Repair or replace
* Replace
* Replace
* Repair or replace
Turn it to the UNLOCK Position.
* Replace
* Adjust
Refill
Clean
Retighten
* Replace
* Replace
* Repair or replace
* Repair or replace
Retighten
* Replace
* Repair or replace
* Replace
* Repair or replace
* Repair or replace
Items with * mark: Consult your authorized dealer.
Solution