Komatsu PC450-6 Fault Code E108: Complete Diagnostic Guide

What is Komatsu PC450-6 Fault Code E108?

Fault Code E108 on the Komatsu PC450-6 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 coolant temperature sensor sending irregular voltage signals outside the manufacturer's specified parameters, typically between 0.5-4.5 volts.

The coolant temperature sensor plays a critical role in the PC450-6's performance by informing the ECM about engine operating temperature. This data directly affects fuel injection timing, idle speed control, and engine protection protocols. When this sensor fails or sends erratic signals, the ECM cannot properly manage engine performance, potentially leading to overheating, poor fuel economy, or engine damage.

Common Symptoms

When Code E108 is active, operators typically experience:

• Engine warning light illuminated on the instrument cluster, often accompanied by a coolant temperature warning
• Hard starting or rough idle, especially when the engine is cold
• Poor fuel efficiency and black smoke from the exhaust due to incorrect fuel mapping
• Engine derate mode activation, limiting power output to prevent potential damage
• Erratic temperature gauge readings that fluctuate abnormally or remain at cold/hot extremes

Potential Causes

The most common technical causes for E108 on used PC450-6 excavators include:

• Faulty coolant temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Damaged wiring harness near the sensor, particularly where the harness contacts the engine block or frame rails
• Corroded or loose electrical connectors at the sensor or ECM connection points
• Shorted or open circuits in the sensor signal wire caused by insulation breakdown
• Low coolant level causing intermittent sensor exposure and false readings
• ECM internal fault (rare, but possible in high-hour machines)

How to Troubleshoot and Fix Code E108

Step 1: Visual Inspection Begin by checking the coolant level in the radiator and overflow tank. Inspect the coolant temperature sensor (typically located on the engine block near the thermostat housing) for physical damage, coolant leaks, or corrosion on the connector. On used excavators, carefully examine the wiring harness for rub-through points, especially where it routes near moving components or sharp edges.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Test the signal wire voltage at the ECM connector with the sensor disconnected—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Circuit and Connector Verification Check for continuity between the sensor connector and ECM pins, and verify there's no short to ground. Clean all connector terminals with electrical contact cleaner and apply dielectric grease. For used machines, replace any connectors showing green corrosion or heat damage.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu coolant temperature sensor (Part #6732-81-3110 or equivalent). After replacement, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then monitor for code recurrence during a complete heat cycle.

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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 heavy equipment repair procedures.