What is Hitachi ZX210LC-5G-HCMC Fault Code 20106-2?

Fault Code 20106-2 indicates a malfunction in the engine coolant temperature sensor circuit, specifically a voltage signal that is reading too low or out of the expected range. This diagnostic trouble code (DTC) is generated by the Engine Control Module (ECM) when it detects an abnormal voltage output from the coolant temperature sensor, typically below 0.2 volts or indicating an open circuit condition.

The engine coolant temperature sensor is critical for the Hitachi ZX210LC-5G-HCMC's Isuzu engine management system. It provides real-time data that the ECM uses to adjust fuel injection timing, control engine warm-up cycles, and manage cooling fan operation. When this sensor fails or provides inaccurate readings, the engine may run inefficiently, consume excessive fuel, or fail to reach optimal operating temperature.

Common Symptoms

• Check Engine Light or malfunction indicator illuminated on the dashboard display
• Engine runs rich or experiences rough idle, especially during cold starts
• Cooling fan runs continuously at high speed, even when engine is cold
• Reduced engine power or performance (derate mode may activate in severe cases)
• Difficulty starting in cold weather conditions due to improper fuel mixture calculations

Potential Causes

The most common causes of Code 20106-2 on used Hitachi excavators include:

• Corroded or damaged sensor connector – particularly common in machines with high hours where moisture has penetrated the electrical connection
• Failed coolant temperature sensor due to internal element degradation
• Wiring harness damage near the engine block where heat and vibration cause insulation breakdown (check routing along the left side of the engine near the thermostat housing)
• Broken or frayed wires between the sensor and ECM, especially at known rub points
• Poor ground connection at the sensor mounting location due to corrosion or loose mounting
• ECM internal fault (rare, but possible in high-hour machines)

How to Troubleshoot and Fix Code 20106-2

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, moisture intrusion, or damaged pins. On used excavators, this connector frequently shows green corrosion. Clean with electrical contact cleaner and check for proper seating.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms. Compare readings to manufacturer specifications. Next, check wiring harness continuity from the sensor connector back to the ECM (typically 5 volts reference signal). Look for voltage drops indicating resistance in the circuit.

Step 3: Sensor and Harness Evaluation Inspect the wiring harness along its entire route, paying special attention to areas where the harness contacts the engine block or frame rails. In used machines, insulation wear at these rub points is extremely common. If wiring appears intact but the sensor tests out of specification, replace the coolant temperature sensor with an OEM or quality aftermarket unit. Clear codes using Hitachi Dr.EX diagnostic software or compatible scan tool and verify repair.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Hitachi service manual for your specific machine serial number and seek assistance from qualified diesel technicians for complex electrical diagnostics or repairs.