What is Komatsu PC120LC-6 Fault Code E108?

Komatsu PC120LC-6 Fault Code E108 indicates a malfunction in the hydraulic pump solenoid circuit, specifically pointing to an abnormal electrical signal between the Engine Control Module (ECM) and the pump control solenoid valve. This code typically represents either an open circuit, short circuit, or resistance value outside the manufacturer's specified range (normally 20-30 ohms) within the hydraulic pump regulation system.

This fault is critical because the pump control solenoid directly regulates hydraulic flow and pressure based on engine load conditions. When E108 is active, the ECM cannot properly modulate hydraulic power delivery, resulting in compromised digging force, reduced fuel efficiency, and potential damage to downstream hydraulic components. On the PC120LC-6's SAA4D102E engine platform, this code directly impacts the electronic load-sensing system that distinguishes Komatsu's sixth-generation machines.

Common Symptoms

• Reduced hydraulic power across all functions (boom, arm, bucket, swing) with noticeably slower cycle times
• Intermittent or constant CHECK ENGINE light illuminated on the instrument cluster
• Erratic engine RPM fluctuations under load, especially during combined hydraulic movements
• Pump whining or cavitation noises due to improper pressure regulation
• Increased fuel consumption as the system defaults to maximum pump displacement mode

Potential Causes

The most frequent technical causes for E108 on used PC120LC-6 excavators include:

• Solenoid coil failure due to age-related insulation breakdown (common after 6,000+ hours)
• Wiring harness abrasion at known rub points: behind the fuel filter assembly and where the harness passes through the bulkhead near the hydraulic tank
• Corroded or moisture-contaminated connectors at the C15 connector (6-pin, located on right side of pump housing)
• Failed ECM output driver circuit within the controller itself (less common but possible on high-hour machines)
• Intermittent ground faults caused by corroded chassis ground points near the battery box

How to Troubleshoot and Fix Code E108

Step 1: Initial Electrical Verification Using a digital multimeter, disconnect the pump solenoid connector (C15) with ignition off. Measure resistance across solenoid terminals—specification is 22-28 ohms at 20°C. Values below 10 ohms indicate internal shorting; above 50 ohms suggests open coil windings.

Step 2: Harness and Connector Inspection On used excavators, physically inspect the entire solenoid harness from ECM to pump. Pay special attention to areas where the harness contacts metal surfaces. Check connector pins for green corrosion or bent contacts—clean with electrical contact cleaner and dielectric grease. Perform a voltage drop test: with ignition on, measure voltage at solenoid connector (should read battery voltage when commanded by ECM).

Step 3: Dynamic Circuit Testing Connect Komatsu KOMTRAX diagnostic software or compatible scan tool. Command the solenoid on/off while monitoring actual vs. commanded state. If ECM commands activation but no voltage appears at the solenoid, trace wiring for breaks. If voltage is present but code persists, replace the solenoid valve assembly (part number 702-16-03011).

Step 4: Ground Circuit Verification Check continuity between solenoid ground pin and chassis ground—should be less than 0.5 ohms resistance. Clean and tighten all ground connections near the hydraulic pump mounting area.

Disclaimer: This guide provides general diagnostic procedures. Hydraulic and electrical system repairs should be performed by qualified technicians with proper training. Always consult the official Komatsu service manual and follow lockout/tagout procedures before performing diagnostics.