What is Komatsu PC120-6 Fault Code E206?

Komatsu PC120-6 Fault Code E206 indicates a malfunction in the hydraulic oil temperature sensor circuit. This fault occurs when the Electronic Control Module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, typically indicating an open circuit, short circuit, or sensor failure.

The hydraulic oil temperature sensor plays a critical role in the PC120-6's operational safety system. It monitors the temperature of the hydraulic oil to prevent overheating, which can lead to reduced hydraulic efficiency, accelerated component wear, and potential system failure. When the ECM cannot reliably read hydraulic oil temperature, it may trigger protective measures to prevent catastrophic damage to the hydraulic system.

Common Symptoms

• Warning light illumination on the instrument panel, often accompanied by an audible alarm
• Engine derate or automatic shutdown in severe cases to protect hydraulic components
• Erratic or missing hydraulic oil temperature readings on the display (showing "--" or unrealistic values)
• Reduced hydraulic performance as the system enters a protective mode
• Intermittent fault activation, especially when the machine vibrates or operates on uneven terrain

Potential Causes

The most common causes of E206 on used PC120-6 excavators include:

• Hydraulic oil temperature sensor failure due to age, heat exposure, or internal component degradation
• Wiring harness damage at known rub points near the hydraulic tank or along the chassis frame
• Corroded or loose electrical connectors at the sensor plug or ECM connection points
• Short circuit to ground caused by damaged wire insulation, particularly common in excavators with 5,000+ operating hours
• ECM internal fault (rare, but possible in high-hour machines with electrical system stress)
• Contaminated sensor threads or improper sensor installation allowing oil leakage and electrical issues

How to Troubleshoot and Fix Code E206

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank). Inspect the sensor connector for corrosion, bent pins, or oil contamination. Check the wiring harness from the sensor to the ECM for visible damage, particularly at flex points and areas where the harness contacts the frame.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. The PC120-6 temperature sensor typically shows 200-300 ohms at 20°C (68°F), increasing with temperature. Compare readings to Komatsu specifications. Check for voltage supply at the connector (typically 5V reference voltage from the ECM). Test for continuity in the wiring harness and verify no short to ground exists.

Step 3: Component Testing and Replacement If the sensor tests outside specifications, replace it with a genuine or OEM-equivalent part. For used excavators, always apply dielectric grease to connectors to prevent future corrosion. If the sensor and wiring test normally, clear the code using Komatsu diagnostic software and monitor for recurrence. Persistent codes after sensor replacement may indicate ECM issues requiring professional diagnostics.

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Disclaimer: This guide provides general troubleshooting information. Always consult a certified Komatsu technician or the official service manual for your specific machine. Improper repairs may void warranties or create safety hazards.