Komatsu PC400LC-6 Fault Code E106: Complete Diagnostic Guide

What is Komatsu PC400LC-6 Fault Code E106?

Fault Code E106 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the Engine Control Module (ECM). This code specifically relates to the temperature monitoring system that protects the Komatsu SAA6D125E-3 engine from overheating damage.

The coolant temperature sensor sends voltage signals to the ECM, which uses this data to regulate fuel injection timing, idle speed, and activate warning systems. On the PC400LC-6, this sensor is critical because improper temperature readings can cause the engine to run in derate mode (reduced power output) or trigger automatic shutdown protocols to prevent catastrophic engine damage. Given that this is a hydraulic excavator, any power reduction directly impacts productivity and cycle times.

Common Symptoms

When Code E106 is active, operators typically experience:

• Engine warning light or coolant temperature warning light illuminated on the monitor panel
• Engine derate mode activated, resulting in significantly reduced hydraulic power and slower cycle times
• Engine running excessively rich or lean due to incorrect temperature compensation
• Hard starting conditions, especially in cold weather, as the ECM cannot properly adjust fuel delivery
• Cooling fans running continuously at maximum speed regardless of actual engine temperature

Potential Causes

The most common technical causes for E106 on used PC400LC-6 excavators include:

• Faulty coolant temperature sensor (common failure point after 8,000+ operating hours)
• Corroded or loose connector at the sensor harness connection point
• Damaged wiring harness between the sensor and ECM, particularly where the harness routes near the engine block (known rub point)
• Low coolant level causing intermittent sensor exposure and erratic readings
• ECM internal fault (less common but possible in high-hour machines)
• Contaminated coolant causing sensor element degradation

How to Troubleshoot and Fix Code E106

Step 1: Visual Inspection Begin by checking coolant level in the radiator and overflow tank. Inspect the coolant temperature sensor (located on the engine block near the thermostat housing) and its connector for corrosion, oil contamination, or physical damage. On used excavators, this connector frequently suffers from moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 20°C (68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness continuity from the sensor connector back to the ECM. Check for short circuits to ground or open circuits.

Step 3: Live Data Analysis Connect Komatsu diagnostic software (KOMTRAX or compatible scan tool) to monitor real-time coolant temperature readings. Compare the displayed temperature against an infrared thermometer reading of the actual coolant temperature. A variance greater than 10°C indicates sensor failure.

Step 4: Repair Actions Replace the coolant temperature sensor if resistance values are out of specification. Clean all connector pins with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Repair any damaged wiring harness sections, paying special attention to areas where the harness contacts the engine block or frame rails—common wear points on older machines.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number. If you lack proper diagnostic tools or experience with high-voltage systems, consult a certified Komatsu technician to avoid injury or further equipment damage.