Komatsu PC400-6 Fault Code E106: Complete Diagnostic Guide

What is Komatsu PC400-6 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. For the PC400-6, this monitoring is critical because the hydraulic system's performance and engine longevity depend heavily on maintaining optimal operating temperatures between 80-95°C (176-203°F).

Common Symptoms

When Code E106 is active, operators typically experience:

• Coolant temperature warning light illuminated on the instrument panel (red or amber)
• Engine derate mode activated, limiting power output to prevent damage
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Cooling fan running continuously at high speed, even during cold starts
• Difficulty starting in cold weather conditions due to incorrect fuel mapping

Potential Causes

The most common technical causes for E106 on used PC400-6 excavators include:

• Faulty coolant temperature sensor (resistance values outside specification range of 200-300 ohms at 80°C)
• Damaged or corroded wiring harness between sensor and ECM, particularly at connector C-103 near the engine block
• Poor ground connection at the sensor mounting point due to corrosion or loose hardware
• Shorted or open circuit in the signal wire, often caused by harness rubbing against engine components
• ECM internal fault (less common, but possible in high-hour machines)
• Actual engine overheating triggering legitimate temperature warnings

How to Troubleshoot and Fix Code E106

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the left side of the cylinder head. Check for physical damage, coolant leaks, or corrosion on the two-pin connector. On used excavators, examine the entire wiring harness from sensor to ECM for chafing, particularly where it passes near the fuel injection pump.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across its terminals. At room temperature (20°C), resistance should read approximately 2,000-3,000 ohms. Compare readings against Komatsu's specification chart. Next, check for continuity in the signal wire from connector to ECM pin B-23, and verify ground integrity (should read less than 1 ohm resistance).

Step 3: Signal Voltage Check With ignition on and sensor connected, back-probe the signal wire at the sensor connector. You should read approximately 5 volts with sensor disconnected, dropping to 0.5-4.5 volts when connected (varying with temperature). Readings outside this range indicate ECM supply issues or internal sensor failure.

Step 4: Component Replacement If testing confirms sensor failure, replace with genuine Komatsu part number 6732-81-3140. Before installation, clean the mounting boss thoroughly and apply anti-seize compound to threads. For harness damage on used machines, repair using heat-shrink solder connectors rather than tape, ensuring waterproof seals.

Step 5: Clear Code and Verify After repairs, use Komatsu diagnostic software (KOMTRAX) or a compatible scan tool to clear the fault code. Run the engine through a complete heat cycle while monitoring live temperature data to confirm proper sensor operation and code elimination.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC400-6 service manual and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.