Hitachi ZAXIS 135US-5B Operator's Manual page 408

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 control shut-off solenoid valve
Faulty wire harness (pilot control shut-off
solenoid valve) pilot control 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 control 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 the pilot control shut-off
lever 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 nearest Hitachi dealer.
Solution