1988 Hitachi EX225USR & EX225USR-LC Excavator Technical Manual – Operational Principle & Troubleshooting (P/N KM-193E)

This Hitachi technical manual, Manual No. KM-193E, covers the EX225USR and EX225USR-LC hydraulic excavators, combining Operational Principle and Troubleshooting volumes with an Operational Principle Training Text.

542 pages in one English-language PDF, including the training text and an additional electrical circuit diagram.

• Engine checks: Factory specifications for the ISUZU A-6BG1T engine, including performance curves and firing order, plus compression testing, valve-clearance adjustment, injection-timing checks and nozzle testing.

• Hydraulic testing: Main-pump flow measurement, primary and secondary pilot-pressure tests, solenoid-pressure adjustment, main/swing/travel relief settings, motor leakage checks and hydraulic-cylinder performance standards.

• Electronic diagnosis: Dr.EX fault-code reading, live monitoring, symptom-based troubleshooting, sensor checks and controller connector pin references for electrical repair decisions.

• Learning and calibration: Engine control strategies covering Auto-Idle, Auto-Warming, and Engine Learning Control sequences, plus Pump Learning Control and A/EC sensor adjustment.

• Swing and travel: Swing device operation, planetary reduction gears, parking brakes, swing bearings and track adjusters, with travel-speed, mistracking and swing-drift tests.

• Circuit references: Wiring diagrams and hydraulic schematics, plus component layouts, sectional views, control-system flowcharts, pump P-Q charts and pilot-valve output diagrams.

Written for experienced technicians carrying out maintenance, troubleshooting and repair on these excavators.

Engine Control and Learning Procedures

The machine controller (MC) coordinates engine speed and hydraulic pump output through sensor inputs, solenoid signals and pump-displacement control.

Engine Learning Control applies after work requiring removal of the engine, control cable or EC motor, and after MC replacement. Pump Learning Control applies after replacing the MC, main pump, PC solenoid valve or regulator; separate procedures describe the rear-console learning switches.

Component layouts distinguish EC-motor arrangements up to serial number 10235 and from 10236 onward. Backhoe and face-shovel specifications are included, with the face shovel defined as a reversed hoe bucket.

Hydraulic Components and Performance Tests

Hydraulic coverage follows the main pumps, pilot circuits and control-valve spools through single and combined machine functions. Flow combiner and arm regenerative valve explanations address combined functions and arm response.

Coverage also includes boom anti-drift valves, shockless valves, pilot shut-off valves, make-up valves, and overload relief valves. The Main Pump P-Q Diagram and Pilot Circuit references complement the control-system explanations for PC/VC solenoid valve units, N sensors and A sensors.

Factory pressure-test specifications, cylinder dimensions, component operating limits and flow measurements support comparison of measured performance with the specified condition. Main-pump flow tests identify the ST6299 portable tester.

Hydraulic pressure tests and raised-track checks require the manual’s pressure-release and machine-support precautions.

Dr.EX Troubleshooting and Electrical Repair

Fault-code troubleshooting is supplemented by symptom-based charts and dedicated monitor/gauge checks. An N-sensor wiring fault can prevent pump learning without producing a fault code; the Dr.EX monitoring guidance helps identify missing engine-speed feedback before a pump repair is considered.

Electrical diagnosis covers starting, charging, preheating and power distribution, with surge voltage protection, accessory supplies and MC connector pin references.

Named references include Starting Circuit, the EC Sensor Failure troubleshooting chart, and the final EX225USR Electrical Circuit Diagram. Sensor, solenoid and EC-motor checks specify dedicated test harnesses, including ST7129 for EC-sensor testing.

During false-signal sensor testing, incorrect terminal grounding can damage the MC, wiring and fuses. The electrical testing section identifies the required connector terminals and precautions.

Repair Scope and PDF Contents

These technical volumes support repair diagnosis through operating principles, performance tests and adjustments. The separate Workshop Manual for removal, installation, disassembly and assembly is not included; internal engine overhaul is also outside this PDF’s coverage.

• Operational Principle — TO193E-00: 152 pages, PDF pages 1–152.

• Operational Principle Training Text — TTLA-390-EX: 139 pages, PDF pages 153–291.

• Troubleshooting — TT193E-00: 250 pages, PDF pages 292–541.

• Electrical Circuit Diagram — WCLA-405-EX: 1 page, PDF page 542.

Page counts include covers, contents pages, blank/memo pages and revision forms. The training text repeats operational-principle material; its pages and the extra circuit diagram are already included in the total.

Embedded bookmarks navigate all four document parts and their listed sections. Text search is limited to the Training Text; the Operational Principle and Troubleshooting volumes and final wiring sheet are not searchable. Small connector numbers and dense wiring labels require zooming.