Komatsu PC120LC-6 Fault Code E-10: Technical Guide

What is Komatsu PC120LC-6 Fault Code E-10?

Fault Code E-10 indicates a malfunction in the engine coolant temperature sensor circuit. This code triggers when the Electronic 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 PC120LC-6's engine management system. It provides real-time data that the ECM uses to adjust fuel injection timing, idle speed, and activate cooling fan operation. When this sensor fails, the engine may run inefficiently or enter a protective derate mode to prevent overheating damage.

Common Symptoms

• Warning light illuminated on the instrument panel, often accompanied by an audible alarm
• Engine running at higher than normal idle speed due to ECM defaulting to cold-start parameters
• Cooling fan running continuously regardless of actual engine temperature
• Black smoke from exhaust due to rich fuel mixture from incorrect temperature readings
• Difficulty starting in cold conditions or extended cranking time

Potential Causes

The E-10 code on used PC120LC-6 excavators typically stems from age-related deterioration:

• Coolant temperature sensor failure - internal resistance drift or complete sensor breakdown (common after 5,000+ hours)
• Wiring harness damage - particularly at the sensor connector near the thermostat housing where vibration and heat cause insulation breakdown
• Corroded or loose connector pins at the sensor plug, especially on machines operated in wet or marine environments
• ECM ground circuit issues - poor chassis ground connections affecting sensor voltage reference
• Coolant contamination on sensor tip causing erratic readings

How to Troubleshoot and Fix Code E-10

Step 1: Visual Inspection Locate the coolant temperature sensor on the engine block near the thermostat housing. Inspect the wiring harness for chafing, burns, or damage from rubbing against engine components. Check the connector for corrosion, bent pins, or coolant intrusion. On used excavators, pay special attention to harness routing where it passes near hot exhaust components.

Step 2: Electrical Testing Disconnect the sensor connector. Using a digital multimeter, measure sensor resistance at various temperatures (typically 2,000-3,000 ohms at 20°C, decreasing as temperature rises). Compare readings against Komatsu specifications. Check wiring continuity from sensor to ECM and verify proper ground circuit resistance (should be less than 5 ohms).

Step 3: Signal Voltage Check With ignition on and sensor connected, backprobe the signal wire at the connector. The ECM supplies approximately 5 volts reference voltage. The sensor should return 0.5-4.5 volts depending on temperature. Readings outside this range indicate sensor or wiring failure.

Step 4: Repair or Replace If wiring and connections test good, replace the coolant temperature sensor with a genuine Komatsu part. After replacement, clear the fault code using diagnostic software and verify proper operation through a heat cycle.

Disclaimer: This guide provides general troubleshooting information. Complex electrical diagnostics should be performed by qualified technicians with proper Komatsu diagnostic equipment. Always consult the official service manual for your specific machine serial number.