Komatsu EX60-3 Dash Lights Staying On With Key Removed

[MikePhua]

Overview of the Issue
Some operators of the Komatsu EX60-3 excavator have reported an unusual condition where multiple dash lights, including battery and oil pressure indicators, remain illuminated even after the ignition key is removed. This scenario is abnormal and indicates a potential electrical or control system fault.
Possible Causes

• Electrical Short or Faulty Wiring: A short circuit or damaged wiring harness in the ignition or dashboard circuit may provide continuous power to the dash lights despite the key being off.
  
• Ignition Switch Malfunction: The key switch itself may be defective or have worn internal contacts that fail to disconnect power when turned off.
  
• Controller Malfunction: The machine’s electronic control unit (ECU) or dashboard control module might be stuck in an active state due to firmware glitches or hardware faults.
  
• Battery Relay Stuck Closed: A stuck relay can maintain power flow to dashboard lights even with the ignition off.
  
• Grounding Issues: Poor grounding or corrosion in electrical connections can create backfeed electrical current causing lights to remain on.
  

Diagnostic Steps

• Inspect the ignition switch operation using a multimeter to check for correct power interruption.
  
• Evaluate key wiring harness and connectors for damage, wear, or corrosion; repair or replace as needed.
  
• Disconnect the battery momentarily to reset control modules and observe if issue resolves, indicating an ECU glitch.
  
• Scan for diagnostic fault codes using machine diagnostics tools; some error codes may hint at electrical system faults.
  
• Test relays related to the ignition and dashboard circuits for proper function and replace faulty units.
  

Temporary Workarounds

• Remove the battery’s negative terminal when machine is parked to prevent battery drain until the root cause is fixed.
  
• Physically unplug dashboard connector to prevent false light illumination if safe to do so.
  
• Consult Komatsu dealer or authorized repair facility for advanced troubleshooting and possible ECU reflashing or replacement.
  

Terminology Explained

• Ignition Switch: The physical switch enabling or disabling power to the vehicle’s electrical system through the key cylinder.
  
• ECU (Electronic Control Unit): Computer that controls engine and machine operations including diagnostic functions.
  
• Relay: Electromagnetic switch controlling high current circuits with low current inputs.
  
• Backfeed: Electrical current flowing into circuits unintentionally due to faults or wiring errors.
  
• Diagnostic Codes: Pre-programmed codes stored in control units indicating the nature of system faults.
  

Recommendations
Prompt electrical system inspection and repair are necessary to prevent battery discharge, false alarms, or potential safety risks. Use of diagnostic tools combined with proper service manuals expedites fault isolation. Regular preventive maintenance of electrical connectors and harnesses can minimize risks of such issues in older excavators.
Conclusion
Persistent dash lighting with the key out on the Komatsu EX60-3 suggests an underlying electrical or control circuit fault. Careful diagnosis focusing on ignition switch functionality, wiring integrity, control unit status, and relay behavior is essential. Addressing these faults restores normal dashboard operation, conserves battery life, and ensures safe equipment readiness.