What is Hitachi ZX210LC-5G-HCMC Fault Code 20105-2?

Fault Code 20105-2 indicates a malfunction in the hydraulic oil temperature sensor circuit, specifically detecting an abnormal voltage signal or open circuit condition in the sensor's electrical pathway. This diagnostic trouble code (DTC) is generated by the machine's Electronic Control Unit (ECU) when it cannot receive valid temperature data from the hydraulic oil temperature sensor, which monitors the operating temperature of the excavator's hydraulic system.

For the Hitachi ZX210LC-5G-HCMC, this sensor plays a critical role in preventing hydraulic system damage. The ECU uses temperature data to trigger warning systems and potentially limit machine performance when hydraulic oil temperatures exceed safe operating ranges. Without accurate readings, the control system cannot protect expensive hydraulic components from overheating damage, making this code particularly important for used machines that may already have accumulated significant operating hours.

Common Symptoms

• Hydraulic oil temperature warning lamp illuminated on the instrument panel, often displaying continuously
• Loss of hydraulic system protection features, potentially allowing operation at dangerous temperatures
• ECU may log the fault without immediate operator notification on some software versions
• Intermittent code activation during cold starts or temperature fluctuations
• Possible activation of derate mode limiting hydraulic flow or engine RPM on some configurations

Potential Causes

The most common causes for Code 20105-2 on used Hitachi excavators include:

Sensor failure due to age, thermal cycling, or internal component breakdown—particularly common on machines exceeding 5,000 operating hours. The hydraulic oil temperature sensor itself can develop internal open circuits or erratic resistance values.

Wiring harness damage is extremely prevalent in used equipment. The harness routing near the hydraulic tank is susceptible to abrasion against the chassis, especially where it passes near mounting brackets or through bulkhead grommets.

Connector corrosion at the sensor plug or ECU interface points. Moisture intrusion from damaged seals or pressure washing creates high-resistance connections that the ECU interprets as sensor failure.

ECU-side circuit issues, including failed input channels or corroded circuit board connections, though less common than field-side problems.

How to Troubleshoot and Fix Code 20105-2

Step 1: Visual Inspection and Connector Examination Begin by locating the hydraulic oil temperature sensor mounted on the hydraulic tank. Disconnect the electrical connector and thoroughly inspect both the sensor-side and harness-side terminals for corrosion, bent pins, or moisture. Clean contacts with electrical contact cleaner and examine the connector seals for damage. On used excavators, this simple step resolves approximately 30% of sensor circuit faults.

Step 2: Sensor Resistance Testing Using a digital multimeter, measure the sensor's resistance across its terminals. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms (consult your specific service manual for exact specifications). Verify the sensor's thermistor response by gently heating it with a heat gun while monitoring resistance—it should decrease smoothly as temperature increases. Erratic readings or open circuit (infinite resistance) indicates sensor replacement is necessary.

Step 3: Harness Continuity and Voltage Testing With the sensor disconnected, check harness continuity from the sensor connector back to the ECU connector. Each wire should show less than 1 ohm resistance to its corresponding ECU pin. Inspect the harness routing carefully for wear points—common damage areas include where the harness crosses the swing bearing and near hydraulic hose bundles. Check for supply voltage (typically 5V reference) at the harness connector with ignition on. Absence of supply voltage indicates an ECU or power supply issue requiring dealer-level diagnostics.

Step 4: Advanced Diagnostics If sensor and wiring test satisfactorily, connect Hitachi diagnostic software (Dr.EX or equivalent) to verify ECU functionality and check for multiple stored codes that might indicate broader electrical system issues. For used machines, perform a complete harness inspection including checking for aftermarket repairs or modified wiring that may cause interference.

---

Disclaimer: This guide provides general troubleshooting information for Code 20105-2. Always consult the official Hitachi service manual for your specific machine serial number. If you're uncomfortable performing electrical diagnostics, or if the fault persists after basic troubleshooting, consult a certified Hitachi technician or qualified heavy equipment mechanic to prevent further damage.