Komatsu PC450-6 Fault Code E106: Complete Diagnostic Guide

What is Komatsu PC450-6 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, fan speed, and engine protection protocols. When the ECM detects voltage readings outside the normal range (typically 0.5-4.5V) or physically impossible temperature values, it triggers E106. For the PC450-6, this is critical because improper temperature management can lead to severe engine damage, reduced hydraulic efficiency, and costly downtime on used machines where sensor degradation is common.

Common Symptoms

• Warning light illuminated on the instrument cluster with possible audible alarm
• Engine derate mode activated, limiting power output to 70-80% capacity
• Cooling fan running continuously at high speed regardless of actual temperature
• Erratic temperature gauge readings or gauge stuck at cold/hot positions
• Difficulty starting when engine is warm, or excessive white smoke during cold starts

Potential Causes

The most frequent causes of E106 on used PC450-6 excavators include:

• Coolant temperature sensor failure due to age-related internal resistance drift (common after 8,000+ hours)
• Corroded or loose connector at the sensor harness (located near the thermostat housing)
• Damaged wiring harness from rubbing against engine components, particularly where the harness routes along the cylinder head
• ECM ground circuit issues causing voltage reference problems
• Contaminated coolant creating sensor tip buildup and false readings
• Failed ECM (rare, but possible on high-hour machines with electrical system history)

How to Troubleshoot and Fix Code E106

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block near the thermostat housing. Inspect the connector for corrosion, bent pins, or moisture intrusion—common issues on used excavators. Check the wiring harness for chafing, especially where it contacts metal surfaces or moves with engine vibration.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across its terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness voltage with the key on, engine off—you should see approximately 5V reference voltage from the ECM. Check for continuity between sensor ground and chassis ground.

Step 3: Component Replacement and Verification If resistance values are out of specification or the sensor shows physical damage, replace it with a genuine Komatsu part (P/N 6732-81-3140 or equivalent). On used machines, always apply dielectric grease to connectors to prevent future corrosion. Clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then monitor for code recurrence during a full heat cycle.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC450-6 service manual and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.