Part of the Hitachi Repair Manuals.
This 451-page Hitachi EX120-2 Technical Manual is the factory reference for your Hydraulic Excavator, covering the EX120 platform from General Information straight through Undercarriage, Electrical, and Hydraulic systems. You get full wiring diagrams with pinout tables, hydraulic schematics tracing every circuit, and a dedicated troubleshooting section that pairs symptoms with actual test values instead of guesswork. Open to the fuels and lubricants chapter and you'll find exact service refill capacities, plus a torque specifications section covering the mono-block control valve and pump assembly. Set hydraulic oil replacement at 2500 hours, and confirm pump axial angle runs 2° to 24° before you chase a phantom fault. Stop swapping parts on a hunch when the machine's down money by the hour. Bookmarked by section and fully text-searchable, this PDF opens on your laptop or phone so you can search any spec by keyword and get back under the boom.
What's Inside This Hitachi EX120-2 Manual
| System | Pages | Key Topics |
|---|---|---|
| Introduction | 1-2 | Safety Alert Symbol, Headline Notation, Technical Manual Updates, How to Use This Manual |
| Safety | 3-13 | High-Pressure Fluid Penetration, Battery Safety, Machine Parking, Burn Prevention, Safe Maintenance Practices |
| Technical Manual: Structure & Function | 14-235 | Specifications, Working Range, Lifting Capacities, Upperstructure, Undercarriage, Hydraulic System, Hydraulic Components, Engine, Electrical System, Attachments |
| Performance Check & Troubleshooting | 236-451 | Operational Performance Tests, Engine Speed and Pump Delivery Checks, Hydraulic Pressure Measurement, Component Troubleshooting, Adjustment Procedures |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Replace Interval for Hydraulic oil | 2500 (Hours) | p. 28 |
| Replace full-flow filter element | 1 | p. 28 |
| Pump axial angle | 2° to 24° | p. 39 |
| Control valve type | mono-block valve with two sections | p. 68 |
| FUSE/5 | 0.5 | p. 143 |
| No.8 fuse | broken | p. 297 |
| Hydraulic oil temperature | 50±5°C (122 ±9°F) | p. 298 |
| Retrial "A" procedure step 3 | After 10 seconds or more have passed, turn ON the key switch or start the engine. | p. 316 |
| Warm-up function will not operate when hydraulic oil temperature is over | 30°C | p. 359 |
| Engine stalls under load | Swash angle at maximum displacement | p. 357 |
| Engine speed for P-mode | 2350±50 rpm | p. 358 |
Hitachi EX120-2 Common Problems This Manual Covers
Hitachi EX120-2 hydraulics become slow after 30-40 minutes of run time while engine runs normally
Check hydraulic oil temperature at the sight gauge; normal range is 50±5°C (122±9°F) per page 298. Past 30°C the warm-up function locks out per page 359. Pull the full-flow filter element for collapse or debris, then drain and refill the 134 liter system per the 2500 hour interval on page 28.
Manual Section: Actuator Malfunctions (A-series) p. 298Main boom becomes weak and loses lifting power after 20-30 minutes of warm operation
Connect a pressure gauge to the boom relief port; system relief pressure should read 350 +20/-0 kgf/cm² per page 240. Cycle the boom cylinder fully to bleed trapped air, then check differential pressure across the cylinder valve, spec ±2 kgf/cm² on page 319. Inspect cylinder rod seals for scoring if the boom still sags.
Manual Section: Actuator Malfunctions (A-series) p. 240Engine stalls under hydraulic pump load while temperature gauge climbs into the red simultaneously
Check the swash plate angle; stalling under load points to the pump swash stuck at maximum displacement per page 357. Verify the pump displacement angle control signal reads over 5 degrees per page 369; a signal stuck low keeps the pump at full stroke and overloads the engine. Inspect the swash plate linkage for binding or seized pivot pins.
Manual Section: Engine Malfunctions (E-series) p. 357Hydraulic speed drops off within 5 minutes of startup, controls feel sluggish
Pull fuse No. 5 (0.5A) from the fuse box per page 143 and check for a broken element; a blown I fuse kills power to the hydraulic control solenoids within minutes. Also inspect fuse No. 8 per page 297. Replace with the same amperage rating, then confirm engine speed holds 2350±50 rpm in P-mode per page 358 before retesting.
Manual Section: Wiring Harness Test p. 143Swash plate binds intermittently, hydraulic response turns erratic across every function at once
Measure pump axial angle travel; full range should sweep 2° to 24° per page 39. A binding swash plate restricts this travel and produces erratic response across every hydraulic function at once. Check the swash plate at the maximum displacement condition referenced on page 357, then inspect the pivot bushings and servo piston for scoring before replacing the pump.
Manual Section: Actuator Malfunctions (A-series) p. 39Frequently Asked Questions
How do I reset Hitachi EX120-2 error codes?
The manual describes two methods to erase fault codes: Retrial "A" for controller problems (PVC and EC) and Retrial "B" for sensor problems. For Retrial "A", turn off the key switch, remove the Dr.EX connector, wait 10 seconds, turn on the key switch, disconnect and reconnect the Dr.EX harness, then recheck. For Retrial "B", leave the key switch ON, disconnect and reconnect the Dr.EX harness after one second, then recheck. Be sure to perform Retrial “A” in order to erase the fault codes in the above cases. p. 316
What do the Hitachi EX120-2 error codes mean?
The manual provides detailed lists of fault codes for both the Engine Controller (EC) and Pump and Valve Controller (PVC). For example, EC fault code 01 indicates "Failure (type-1) of EC", while PVC fault code 22 indicates "Abnormal pump control". Each code is accompanied by a description of the trouble and recommended corrective actions, found on pages 333-334. p. 333
Where is the PVC module located on the Hitachi EX120-2?
The Pump and Valve Controller (PVC) module is located in the operator's cab, specifically underneath the Engine Controller (EC) and behind the operator's seat. The Dr.EX diagnostic connector is also located behind the operator's seat, connected to the PVC, as described on page 314. p. 164
What are the replacement specifications for the Hydraulic pump?
The manual does not provide specific replacement specifications for a full rebuild of the hydraulic pump. However, it indicates that the pump should be changed if it fails to meet the specified flow rates during performance tests, such as delivering 201 L/min at 0 kgf/cm2 pressure, as detailed in the PUMP PQ CURVE on page 245. p. 295
How quickly can I access this Hitachi EX120-2 manual after buying?
Immediate download of the complete 451-page searchable Technical Manual. Access it on any device, from a laptop at your desk to a phone in the field.
Can I print this Hitachi EX120-2 manual?
Absolutely. No DRM or copy protection. Print the whole manual or just the pages you need. Any home or office printer works.
Does this Hitachi EX120-2 manual include hydraulic schematics?
Included. A hydraulic system diagram shows the main hydraulic layout for the Hitachi EX120-2.
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