Hitachi EX and ZX excavators became some of the best-known hydraulic excavators in construction, quarrying, utilities and general earthmoving. Models such as the EX100, EX120, EX200, ZX120, ZX130 and ZX200 represent generations of machines that combine strong undercarriages with sophisticated hydraulic pump, pilot and electronic control systems.
This guide covers Hitachi EX and ZX mid-size excavators in general. Hydraulic pump arrangements, pilot pressures, electronic controllers, travel motors, swing systems, undercarriages and fault-code systems vary by model, suffix and serial range. Use the exact workshop manual for all pressure, adjustment and calibration data.
1. The Hitachi EX and ZX Families
Common mid-size models include:
- EX100 / EX120
- EX150 / EX160
- EX200
- ZX110 / ZX120 / ZX130
- ZX160 / ZX180
- ZX200 and related versions
The model families span different generations and should not be treated as mechanically identical.
2. Identification Before Repair
Record:
- Exact model
- Serial number
- Engine model
- Hydraulic pump identification
- Travel-motor/final-drive type
- Controller/display version
A change in serial range can mean different pumps, regulators, sensors, wiring, travel motors or pressure settings even within the same basic model.
3. Diesel Engine
Different generations use different diesel engine families.
When assessing the engine, check:
- Cold starting
- Oil pressure
- Blow-by
- Exhaust smoke
- Coolant condition
- Fuel, oil and coolant leaks
4. Hard Starting
Check:
- Battery condition
- Starter cranking speed
- Fuel filters
- Air in fuel system
- Cold-start system
- Compression
- Injection-system condition
5. Cooling System
Excavators often work in dust, mud and restricted airflow.
Inspect:
- Radiator
- Hydraulic oil cooler
- Intercooler where fitted
- Fan and belt system
- Coolant hoses
- Cooler screens
6. Cooler Pack Blockage
Dirt between coolers can cause:
- Engine overheating
- Hydraulic overheating
- Reduced power
Clean the complete cooler pack, not only the visible outer surface.
7. Main Hydraulic Pumps
Many Hitachi excavators use variable-displacement piston pumps.
Depending on model, pump control may involve:
- Pump regulators
- Pressure-compensating control
- Engine speed sensing
- Electronic pump control
- Power-mode selection
8. What the Pump Regulator Does
The regulator changes pump displacement according to machine demand and available engine power.
Incorrect adjustment can cause:
- Engine lugging
- Weak hydraulics
- Slow cycle times
- Excessive fuel use
9. All Hydraulic Functions Weak
Check:
- Hydraulic oil level
- Pump inlet restriction
- Filter condition
- Pilot pressure
- Main pump output
- Main relief pressure
- Pump-control signals
10. Hydraulics Strong Cold but Weak Hot
Possible causes include:
- Internal pump leakage
- Control-valve leakage
- Worn cylinders
- Incorrect oil
- Relief-valve leakage
11. Engine Lugs Heavily During Hydraulic Operation
Possible causes include:
- Pump over-stroking
- Pump regulator fault
- Incorrect control pressure
- Electronic pump-control fault
- Engine power problem
12. Pilot Hydraulic System
The operator controls commonly use low-pressure pilot oil to shift the main control valve.
Pilot oil may also operate:
- Travel controls
- Swing controls
- Safety lock circuit
- Auxiliary controls
13. Low Pilot Pressure
Possible symptoms include:
- All functions slow to respond
- Some spools not moving fully
- Controls feel inconsistent
- Machine stops responding after warm-up
14. Pilot Shut-Off / Safety Lever
The safety lever disables hydraulic pilot controls when raised.
If the machine has no hydraulic response, check:
- Safety-lever switch
- Pilot shut-off valve
- Electrical interlock
- Pilot pressure
15. Main Control Valve
The main valve directs oil to:
- Boom cylinders
- Arm cylinder
- Bucket cylinder
- Swing motor
- Travel motors
- Auxiliary circuits
16. One Function Weak
If the other functions are strong, investigate:
- Relevant spool section
- Port relief valve
- Cylinder leakage
- Hoses
- Pilot signal to that spool
17. Boom Drifts Down
Possible causes include:
- Boom-cylinder internal leakage
- Main control-valve leakage
- Load-holding valve fault where fitted
18. Arm or Bucket Drifts
Use a controlled drift test to separate:
- Cylinder bypass
- Control-valve leakage
- Port-valve leakage
19. Hydraulic Oil Overheating
Possible causes include:
- Relief valve operating continuously
- Internal leakage
- Blocked oil cooler
- Pump control fault
- Incorrect oil
20. Swing System
The swing system normally includes:
- Swing motor
- Swing reduction gearbox
- Brake
- Relief/cushion valves
- Slew ring
21. Swing Slow or Weak
Check:
- Pilot signal
- Main pressure
- Swing motor leakage
- Swing relief valves
- Mechanical resistance
22. Swing Creep
Possible causes include:
- Swing brake leakage
- Control-valve leakage
- Pilot valve not fully centring
23. Slew Ring
Inspect:
- Lubrication
- Bolt condition
- Excessive play
- Abnormal noise
- Ring gear condition
Do not guess torque or allowable movement. Use the exact machine manual and approved measuring procedure.
24. Travel System
Each track is generally driven by:
- Travel motor
- Reduction final drive
- Sprocket
Oil passes to the motors through the centre joint.
25. Machine Travels Slowly
Check:
- Engine speed
- Pilot pressure
- Main pump output
- Travel pressure
- Travel motor case drain
- Track tension
- Mechanical drag
26. One Track Slower Than the Other
Possible causes include:
- Travel motor wear
- Pump imbalance
- Control-valve leakage
- Centre-joint leakage
- Track or undercarriage drag
27. Final Drives
Inspect final-drive oil for:
- Correct level
- Metal contamination
- Water contamination
- Burnt smell
Check for leaks around the drive housing.
28. Final Drive Noise
Grinding, knocking or rumbling can indicate:
- Bearing wear
- Gear damage
- Low oil
- Planetary damage
29. Centre Joint
The centre swivel transfers hydraulic oil between the upper structure and undercarriage while allowing the upper body to rotate.
30. Centre-Joint Leakage Symptoms
Possible symptoms include:
- One travel function weak
- Machine veers
- Travel cross-feeding
- Oil leakage at the centre
31. Undercarriage
Inspect:
- Track chains
- Pins and bushes
- Sprockets
- Bottom rollers
- Top rollers
- Idlers
- Track adjusters
32. Track Tension
Track sag must be set to the correct specification for:
- Machine model
- Track type
- Working conditions
Too tight increases wear; too loose risks derailment.
33. Grease Track Adjuster
Track tension is commonly adjusted using grease pressure.
Track adjusters can contain very high stored pressure. Follow the exact pressure-release procedure and never place your body in line with the valve or adjuster components.
34. Recoil Spring
The recoil spring stores very high mechanical energy.
Do not dismantle a recoil assembly without the correct tooling and service procedure.
35. Track Chain and Sprocket Wear
Wear accelerates when:
- Tracks are too tight
- Machine travels long distances
- Undercarriage is packed with material
- Machine constantly works on one side of a slope
36. Boom, Arm and Bucket Pins
Inspect:
- Pins
- Bushes
- Bosses
- Seals
- Grease passages
37. Excessive Front-End Play
Worn pins and bushes can cause:
- Poor digging accuracy
- Shock loading
- Cracked bosses
- Accelerated cylinder-end wear
38. Structural Inspection
Inspect:
- Boom foot
- Boom centre sections
- Arm
- Bucket linkage
- Counterweight area
- Carbody and track frames
39. Electrical and Electronic Controls
Later machines may use controllers for:
- Engine speed
- Pump control
- Work modes
- Travel speed
- Auto-idle
- Monitoring and fault codes
40. Auto-Idle Faults
Possible causes include:
- Pressure/switch input fault
- Engine-speed control problem
- Controller fault
- Wiring issue
41. Work-Mode Problems
If a machine feels weak in one mode but normal in another, investigate:
- Mode switch
- Pump-control solenoids
- Controller commands
- Engine-speed signal
42. Fault Codes
Later ZX machines may record faults involving:
- Engine
- Hydraulic pump control
- Pressure sensors
- Speed sensors
- CAN communication
- Solenoids
Record the exact code and operating condition before clearing it.
43. Low Battery Voltage
Poor battery voltage or earth connections can cause:
- Multiple fault codes
- Slow cranking
- Controller resets
- Intermittent solenoid operation
44. Auxiliary Hydraulic Circuits
Excavators may be equipped for:
- Hydraulic breakers
- Thumbs
- Shears
- Rotators
- Other attachments
45. Breaker Circuit Setup
Breaker operation may require the correct:
- Flow setting
- Pressure setting
- Return arrangement
- Accumulator arrangement where applicable
Incorrect setup can damage both attachment and excavator.
46. Hydraulic Accumulator Safety
Follow the manufacturer’s pressure-release procedure before opening pilot or hydraulic circuits.
47. Long-Storage Problems
- Contaminated diesel
- Corroded electrical connectors
- Hydraulic hose deterioration
- Cylinder seal leakage
- Final-drive oil contamination
- Track adjuster corrosion
- Sticking control valves
48. Before First Start After Storage
- Identify exact machine and serial range.
- Check engine oil and coolant.
- Inspect fuel and filters.
- Check hydraulic oil.
- Check final-drive oils.
- Inspect hoses and cylinders.
- Inspect undercarriage and track tension.
- Check slew ring lubrication and visible bolts.
- Inspect electrical system.
- Run functions slowly and check for abnormal noises or leaks.
49. Buying a Used Hitachi EX / ZX
Check:
- Exact model and serial number
- Cold starting and engine blow-by
- Hydraulic speed hot and cold
- Engine lugging under hydraulic load
- Travel straightness
- Final-drive noise and leaks
- Swing play and creep
- Slew-ring movement
- Boom/arm/bucket pin wear
- Track-chain and sprocket condition
- Warning lights and fault codes
50. Repair and Restoration Priorities
- Identify model and serial range.
- Make engine and cooling system reliable.
- Service hydraulic oil and filters.
- Test pilot and main hydraulic pressures correctly.
- Check pump control before condemning the pumps.
- Repair travel/final-drive faults.
- Repair swing and slew-ring wear.
- Repair pins, bushes and undercarriage.
- Repair electrical and controller faults.
- Finish cosmetic work last.
51. Workshop Checklist
| System | Check |
|---|---|
| Identification | Exact model and serial range confirmed. |
| Engine | Cold start, smoke, oil pressure and blow-by. |
| Main hydraulics | Pump control, pressures and cycle speed correct. |
| Pilot system | Correct pressure and safety shut-off operation. |
| Travel | Tracks run evenly; final drives quiet and leak-free. |
| Swing | No excessive creep, noise or slew-ring play. |
| Undercarriage | Track chain, sprockets, rollers and idlers serviceable. |
| Front attachment | Pins, bushes, cylinders and structure sound. |
| Electronics | No unresolved active fault codes. |
Related Agrimanual Manuals
- Search Agrimanual Hitachi EX120 manuals
- Search Agrimanual Hitachi EX200 manuals
- Search Agrimanual Hitachi ZX120 manuals
- Search Agrimanual Hitachi ZX200 manuals
- Request a Hitachi excavator manual for your exact model and serial range
Frequently Asked Questions
Why are all hydraulic functions slow on a Hitachi excavator?
Check pilot pressure, pump supply, main pump control, filters and main pressure before assuming both pumps are worn out.
Why does one track run slower than the other?
Possible causes include travel-motor wear, pump imbalance, centre-joint leakage, control-valve leakage or mechanical undercarriage drag.
Why does the engine nearly stall when I operate the hydraulics?
The pump may be demanding too much power, or the engine may not be producing full power. Check pump regulation and engine performance together.
Why does the upper structure creep when the swing control is neutral?
Possible causes include swing brake leakage, control-valve leakage or pilot-control problems.
Can I release track tension by removing the grease valve completely?
No. Follow the exact high-pressure grease release procedure in the workshop manual. Track adjusters can store dangerous pressure.
Hitachi EX and ZX excavators are durable machines, but their hydraulic performance depends on the relationship between engine power, pump regulation, pilot pressure and electronic control. Methodical testing can prevent extremely expensive pump or motor replacement when the real fault lies elsewhere.