Komatsu PC120-6 Fault Code E106: Complete Technical Guide

What is Komatsu PC120-6 Fault Code E106?

Fault Code E106 indicates a hydraulic pump control solenoid circuit malfunction in the Komatsu PC120-6 excavator. This code specifically relates to an abnormal voltage signal detected by the Engine Control Module (ECM) in the circuit controlling the main hydraulic pump's displacement solenoid valve.

The PC120-6 uses an electronically controlled hydraulic pump system that adjusts oil flow based on load demands. The pump control solenoid receives variable voltage signals from the ECM to regulate pump displacement angle. When the ECM detects voltage outside normal operating parameters (typically 0.5-4.5V), it triggers E106 and stores the fault in memory. This is critical because improper pump control directly affects hydraulic power, fuel efficiency, and overall machine productivity.

Common Symptoms

• Reduced hydraulic power across all functions (boom, arm, bucket, swing)
• Engine over-revving without corresponding hydraulic speed increase
• Amber warning light illuminated on instrument panel
• Sluggish or erratic operation when performing combined functions
• Increased fuel consumption due to inefficient pump operation

Potential Causes

The most common technical failures triggering E106 in used PC120-6 excavators include:

• Solenoid coil failure within the pump control valve assembly (resistance typically measures 10-15Ω when functional)
• Harness wiring damage near the pump mounting area where cable routing creates friction against chassis components
• Connector corrosion at the 6-pin pump solenoid connector (common moisture ingress point)
• ECM internal driver circuit failure (less common but known issue in high-hour machines)
• Grounding issues caused by corroded ground terminals on the hydraulic pump housing

How to Troubleshoot and Fix Code E106

Step 1: Visual Inspection Inspect the pump solenoid harness from ECM to pump for visible damage, chafing, or burnt insulation. On used excavators, check the harness routing near the swing motor mounting bracket—a known wear point. Examine the connector terminals for green corrosion or pushed-back pins.

Step 2: Electrical Testing Using a digital multimeter, disconnect the pump solenoid connector and measure coil resistance (should read 10-15Ω). Check for short to ground (should show infinite resistance). With ignition ON, measure supply voltage at the harness connector (should read battery voltage momentarily during startup).

Step 3: ECM Signal Verification Using Komatsu diagnostic software (KDW or compatible scan tool), monitor real-time pump control signal output while operating functions. Signal should vary smoothly between 0.5-4.5V under load. Erratic readings indicate ECM driver failure.

Step 4: Component Replacement Replace faulty components in this order: solenoid coil assembly, harness repair/replacement, ECM (if driver circuit confirmed failed). For used machines, always apply dielectric grease to connectors during reassembly to prevent future corrosion.

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Disclaimer: This guide provides general diagnostic information. Excavator repairs involve high-pressure hydraulics and electrical systems. Consult qualified technicians and refer to official Komatsu service manuals before attempting repairs.