EX60 Travel Controls Not Functioning

[MikePhua]

Engine Rehabilitation and Control Challenges
A Hitachi EX60-2 excavator had its original engine damaged in a rollover and was replaced with a Kubota power unit. In the process, the electronic throttle control (EC motor) and EPC system were bypassed in favor of a manual lever, resulting in constant full-power operation. Now, although the machine runs strongly at wide-open throttle, it struggles and becomes jerky at lower settings. Control panel buttons—including Power (P), Economy (E), and other functions (I, L)—fail to light or change behavior, and travel speed remains unresponsive despite indicator illumination.
Key Components Explained

• EC Motor (Electronic Control Motor): Adjusts throttle via electronic signals rather than direct mechanical linkage.
  
• EPC System: Controls engine speed and hydraulic pump swash angle electronically to match performance modes.
  
• Fuses (1 Amp): Small electrical fuses that safeguard the EC/EPC circuits; failure can disable system responsiveness.
  
• PWM (Pulse-Width Modulation): Solenoids may use rapid on-off switching (not continuous voltage) to adjust pressure or pump displacement—making standard voltage measurement ineffective.
  

Diagnostic Journey
Initial probing revealed no visible harness damage, but access was hindered by generic multimeter probes. After obtaining fine-tipped probes, the owner tested the circuits. A previously intact-looking 1 Amp fuse was identified as faulty, and upon replacing it, the EPC light began blinking and the throttle motor responded to panel inputs. All travel modes also became operational.
However, pressing the Economy (E) mode caused the engine to lug heavily while hydraulics surged—contrary to expected behavior. Voltage testing showed about 1.6 V on one solenoid pin and a steady 24 V on the other, regardless of mode—a puzzling result until further analysis.
Electronic Control Insight
In the EX60-2, the pump displacement solenoids are simple on/off types, not proportional. They are constantly supplied with 24 V when the key is on; the control unit switches ground via PWM to modulate. This means that using a voltmeter alone may mislead; instead, you must observe blinking lights (indicating electronic modulation) or use a duty-cycle capable meter. The wiring chart clarifies how travel mode (Fast/Medium/Slow) and mode selection (P/E/L) interact to vary engine speed and solenoid state. For example:

• In P mode with Fast travel, engine runs at full RPM and solenoid is off.
  
• Pressing E lowers engine speed and switches solenoid on or off depending on travel speed.
  

Technical Snapshot

• Excavator: Hitachi EX60-2
  
• Engine swap: Replaced with Kubota, bypassed EC/EPC system
  
• Fault: Full-power lock, non-functional control panel buttons
  
• Fix: Replaced a blown 1 Amp fuse restoring EPC light, button response, and throttle motor operation
  
• Anomaly: E mode causes engine lug and hydraulic speed rise
  
• Wiring note: Solenoids use PWM; not simply voltage-driven
  

Tips and Recommendations

• Always inspect small fuses—even when they appear intact with a multimeter—since they can fail subtly.
  
• For PWM-controlled solenoids, use a duty-cycle or oscilloscope measurement—or judge proper function by panel light flickering.
  
• After restoring electrical functions, perform a manual throttle relearn or reset procedure to sync the ECU and new control components.
  
• Examine and replace any partially collapsed hoses (like the pilot pump suction hose) that might impair hydraulic responsiveness.
  
• Reference wiring charts carefully to understand the P/E/L + travel mode interactions; follow the logic for proper solenoid control.
  

A Real-World Glimpse
An operator shared that once the fuse was replaced, the control panel came alive—lights flickered, and response was restored. It felt like waking a sleeping system back to life, transforming the machine from erratic and unpredictable into responsive again. The experience underlines how a seemingly minor part—a low-amp fuse—can be the linchpin in complex electronic-hydraulic systems.
Conclusion
Modern excavator control systems, like those in the EX60-2, rely on coordinated electrical and hydraulic components. Problems may not stem from complex failures but from simple items like a fuse or unplugged harness. Diagnosing PWM-based solenoids demands careful methodology, often involving visual or duty-cycle observations rather than raw voltage checks. With patient testing, wiring insight, and small parts inspection, even a rewired machine can regain full, smooth control.