What is Komatsu PC100-6 Fault Code E103?

Komatsu PC100-6 Fault Code E103 indicates a malfunction in the engine coolant temperature sensor circuit. This diagnostic trouble code is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, typically caused by an open circuit, short circuit, or sensor failure.

The coolant temperature sensor is critical for the PC100-6's performance because it directly influences fuel injection timing, engine warm-up cycles, and protective shutdown systems. When this sensor fails, the ECM cannot accurately monitor engine temperature, potentially leading to overheating, poor fuel economy, or engine damage. For used excavators, this code often appears due to age-related degradation of wiring insulation or corrosion at sensor connectors.

Common Symptoms

• Engine warning light illuminated on the instrument panel, sometimes accompanied by a beeping alarm
• Hard starting or extended cranking time, especially in cold conditions
• Black smoke from the exhaust due to improper fuel mixture adjustment
• Engine operating in derate mode with reduced power output to protect internal components
• Cooling fan running continuously at high speed regardless of actual engine temperature

Potential Causes

The most common technical causes for E103 on used PC100-6 excavators include:

• Coolant temperature sensor failure due to internal element degradation after prolonged exposure to heat cycles
• Damaged wiring harness near the sensor location, particularly where the harness routes along the engine block and experiences vibration or heat exposure
• Corroded or loose connector pins at the sensor plug, extremely common in machines operating in humid or marine environments
• ECM internal fault affecting the sensor input circuit (less common but possible in high-hour machines)
• Ground circuit issues causing voltage reference problems between the sensor and ECM

How to Troubleshoot and Fix Code E103

Step 1: Visual Inspection Locate the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness for signs of abrasion, melting, or rodent damage. Check the connector for corrosion, moisture, or bent pins—this is particularly important on used excavators where exposure to harsh environments is common.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 68°F (20°C), resistance should typically read between 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 5 volts at the connector from the ECM.

Step 3: Circuit Verification Check for continuity between the sensor connector and the ECM pins using wiring diagrams. Look for resistance below 1 ohm on good circuits. Inspect ground circuits carefully, as corrosion at grounding points frequently causes intermittent faults on older machines.

Step 4: Component Replacement If sensor resistance is out of specification or harness damage is found, replace the faulty component. Always apply dielectric grease to connectors during reassembly to prevent future corrosion. Clear codes using Komatsu diagnostic software or a compatible scan tool, then verify repair by monitoring live sensor data during engine warm-up.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional assistance for complex electrical diagnostics.