What is Hitachi ZX200LC-5G Fault Code 20105-2?

Fault Code 20105-2 on the Hitachi ZX200LC-5G indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open circuit condition. This code is registered by the machine's Electronic Control Module (ECM) when the coolant temperature sensor fails to provide accurate readings within the manufacturer's specified voltage range (typically 0.5-4.5V).

This fault is critical for the ZX200LC-5G's performance because the ECM relies on precise coolant temperature data to optimize fuel injection timing, regulate engine speed, and prevent overheating. When this sensor circuit malfunctions, the engine may enter a protective derate mode, limiting power output to prevent catastrophic damage. For used excavators, this code often appears due to sensor degradation, corroded connectors, or harness damage from years of exposure to vibration and environmental stress.

Common Symptoms

• Yellow or amber engine warning light illuminated on the instrument panel
• Engine derate mode activated, limiting maximum RPM to 1,500-1,800 range
• Poor cold-start performance or extended cranking time in low temperatures
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Erratic temperature gauge readings or gauge stuck at minimum/maximum position

Potential Causes

The most common technical causes for Code 20105-2 on used ZX200LC-5G excavators include:

• Coolant temperature sensor failure due to internal resistance drift or element corrosion
• Damaged wiring harness near the engine block where vibration causes wire chafing against metal surfaces
• Corroded or loose connector pins at the sensor plug, especially on machines operated in wet or coastal environments
• Open circuit in the signal wire between the sensor and ECM (common failure point behind the fuel filter housing)
• ECM internal circuit fault (rare, but possible on high-hour machines)
• Intermittent ground connection caused by loose chassis ground straps

How to Troubleshoot and Fix Code 20105-2

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the connector for corrosion, moisture, or damaged pins. Check the wiring harness along its entire length for abrasion points, particularly where it contacts the engine or frame. On used excavators, pay special attention to harness routing near moving components.

Step 2: Electrical Testing Disconnect the sensor and measure resistance across the sensor terminals using a digital multimeter. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult service manual for exact specifications). Next, check for continuity between the sensor connector pins and the ECM connector to identify open circuits. Measure supply voltage at the sensor connector with ignition on—should read approximately 5V.

Step 3: Component Replacement and Verification If testing reveals sensor failure, replace with a genuine Hitachi part or OEM-equivalent. Clean connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. After installation, clear fault codes using Hitachi diagnostic software (Dr.EX) or compatible scan tool. Test-run the machine through temperature cycles to verify proper operation.

Disclaimer: This guide provides general troubleshooting information. For complex electrical issues or if you're unfamiliar with diagnostic procedures, consult a certified Hitachi technician or authorized service center to prevent incorrect repairs or safety hazards.