Diagnosing Hydraulic and Electrical Failure in a Hitachi EX200-2

[MikePhua]

Hitachi EX200-2 and Its Legacy
The Hitachi EX200-2 excavator, launched in the late 1980s, became one of the most widely used mid-size hydraulic excavators in Asia, Africa, and South America. Built for durability and simplicity, it featured a mechanical fuel injection system, analog control circuits, and a robust hydraulic platform. Hitachi Construction Machinery, founded in 1970, designed the EX200 series to meet the growing demand for reliable earthmoving equipment in developing markets. By the mid-1990s, the EX200-2 had sold tens of thousands of units globally, often outlasting newer models due to its rebuild-friendly architecture.
Symptoms of Combined Hydraulic and Electrical Failure
A common issue with aging EX200-2 units is simultaneous failure of hydraulic and electrical systems after prolonged inactivity. In one case, an excavator that had sat idle for over a year was restarted only to experience immediate hydraulic loading—where the pumps engage fully without operator input—and a dead controller panel with no indicator lights. This dual failure suggests a breakdown in the machine’s electronic control interface, which governs pump swash plate angle and valve actuation.
Rodent Damage and Wiring Vulnerability
Excavators stored outdoors or in barns are susceptible to rodent infestation. Mice and rats often chew through wiring harnesses, especially behind the operator seat and under the floor panels. These harnesses carry signals from the controller to the hydraulic solenoids and sensors. A chewed wire can short the system, causing the pumps to default to full stroke, which stalls the engine under load. Technicians should inspect:

• Harnesses behind the seat and under the cab
  
• Relay boxes and fuse panels
  
• Grounding points and battery terminals
  

Rodent damage is often invisible until panels are removed. A flashlight and mirror can help trace compromised wires in tight spaces.
Relay and Fuse Testing Procedures
The EX200-2 uses standard automotive-style relays and blade fuses. If the controller panel is unresponsive, technicians should:

• Test all fuses with a multimeter (not just visual inspection)
  
• Swap relays with known good units to rule out internal failure
  
• Check for voltage at the controller input terminals
  
• Verify that the key switch is sending power to the relay coil
  

Relays can fail silently, especially after long periods of disuse. Corrosion inside the relay contacts may prevent activation even if the coil energizes.
Hydraulic Loading and Pump Control Circuit
The EX200-2’s hydraulic system uses a variable displacement pump controlled by an electrical signal that adjusts the swash plate angle. If the controller fails or loses power, the pump may default to maximum displacement, causing the engine to stall under load. This condition is known as “hydraulic lock” and can be mitigated by:

• Disconnecting the pump control solenoid to force neutral
  
• Manually adjusting the swash plate if accessible
  
• Using a diagnostic jumper to simulate controller output
  

In some cases, the pump control valve may stick due to varnish or debris. A flush with clean hydraulic fluid and manual cycling can restore function.
Jump Starting and Voltage Spikes
Jump starting an excavator with a weak battery can introduce voltage spikes that damage sensitive electronics. If the EX200-2 was jump-started, technicians should inspect:

• Controller board for burn marks or capacitor bulging
  
• Voltage regulator and alternator output
  
• Battery health and terminal corrosion
  

A surge protector or battery isolator is recommended when jump-starting older machines. In one documented case, a jump start caused a controller failure that cost over $2,000 to replace.
Recommendations for Recovery and Repair
To restore an EX200-2 with hydraulic and electrical failure:

• Begin with a full visual inspection for rodent damage
  
• Test and replace fuses and relays systematically
  
• Verify controller power and ground connections
  
• Isolate hydraulic pump control circuits to prevent engine stall
  
• Avoid jump starts without surge protection
  

If the controller is confirmed dead, replacement units are available from rebuilders in Japan and the U.S., often with updated firmware and reinforced solder joints.
Conclusion
The EX200-2 remains a workhorse in many fleets, but its age makes it vulnerable to electrical and hydraulic faults—especially after long storage. With methodical troubleshooting and attention to wiring integrity, most issues can be resolved without major component replacement. The key is understanding the interplay between electrical signals and hydraulic behavior, and respecting the machine’s original design logic.