What is Hitachi ZX360H-5G Fault Code 20105-2?

Fault Code 20105-2 on the Hitachi ZX360H-5G indicates a malfunction in the engine coolant temperature sensor circuit, specifically a voltage signal that is out of normal operating range (typically too high). This code is triggered when the Engine Control Module (ECM) detects an abnormal voltage reading from the coolant temperature sensor, which monitors the engine's thermal status to optimize fuel injection, timing, and protect against overheating.

The coolant temperature sensor is critical for the Isuzu engine found in the ZX360H-5G model. It provides real-time data that allows the ECM to adjust engine parameters for efficient combustion and prevent thermal damage. When this sensor circuit fails, the ECM cannot accurately manage engine temperature, potentially leading to reduced performance, increased emissions, or even catastrophic engine damage if overheating goes undetected.

Common Symptoms

When fault code 20105-2 is active, operators may experience:

• Check Engine Light or engine warning lamp illuminated on the instrument panel
• Engine derate mode where power output is reduced to protect the engine from potential thermal damage
• Hard starting or rough idle, especially during cold starts when accurate temperature readings are most critical
• Poor fuel economy due to the ECM defaulting to a safe but inefficient fuel map
• Cooling fan running continuously at high speed as the ECM assumes worst-case temperature conditions

Potential Causes

The most common technical reasons for code 20105-2 on used ZX360H-5G excavators include:

• Failed coolant temperature sensor due to internal element degradation or contamination from old coolant
• Damaged wiring harness between the sensor and ECM, particularly at flex points near the engine block where vibration causes wire fatigue
• Corroded or loose electrical connectors at the sensor or ECM, especially on machines operated in wet or corrosive environments
• Broken or chafed wires where the harness contacts sharp edges or moving components during engine operation
• ECM internal fault (rare) affecting the temperature sensor input circuit
• Poor ground connection at the sensor mounting point due to rust or improper installation during previous repairs

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 sensor connector for corrosion, bent pins, or moisture intrusion. Check the wiring harness from the sensor to the ECM for obvious damage, chafing against metal surfaces, or signs of previous repairs. On used excavators, pay special attention to areas where cable ties may have deteriorated, allowing wires to rub against engine components.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness continuity from the sensor connector to the ECM pins, checking for opens or shorts to ground. Measure voltage supply at the sensor connector with the key on, engine off—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Component Replacement and Verification If the sensor tests out of specification or the harness shows damage, replace the faulty component using genuine Hitachi or OEM-equivalent parts. When installing a new sensor, apply a small amount of anti-seize compound to the threads and ensure the electrical connector is fully seated with the locking tab engaged. Clear the fault code using Hitachi Dr.EX diagnostic software or a compatible scan tool, then operate the machine through a full heat cycle to verify the repair. Monitor coolant temperature readings in real-time to confirm they match actual engine conditions.

---

Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the official Hitachi service manual for your specific machine serial number and seek assistance from certified technicians when working with engine management systems. Improper diagnosis or repairs may result in equipment damage or safety hazards.