What is Hitachi ZX690LCH-5A Fault Code 20107-2?

Fault Code 20107-2 indicates a malfunction in the hydraulic oil temperature sensor circuit, specifically a voltage signal that is too high or out of normal operating range. This Diagnostic Trouble Code (DTC) is triggered when the Engine Control Module (ECM) or Machine Controller detects an abnormally high voltage reading from the hydraulic oil temperature sensor, typically exceeding 4.5 volts on the sensor signal wire.

This code is critical for the ZX690LCH-5A because hydraulic oil temperature directly affects system efficiency, component longevity, and operational safety. When the controller cannot accurately monitor oil temperature, the machine may enter derate mode to prevent thermal damage to pumps, motors, and seals. On used excavators, this sensor circuit is particularly vulnerable to deterioration from years of exposure to heat, vibration, and environmental contamination.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the instrument panel (amber or red)
• Reduced hydraulic performance or machine entering protective derate mode limiting arm/bucket speed
• Erratic temperature gauge readings that jump between extremes or show constant maximum temperature
• ECM storing active fault codes with corresponding malfunction indicator lamp (MIL) activation
• Cooling fan running continuously at high speed even during cold startup conditions

Potential Causes

The most common technical causes for Code 20107-2 on used ZX690LCH-5A excavators include:

• Open circuit in sensor wiring harness due to wire breakage, particularly at flex points near the hydraulic tank or along the boom base where harnesses experience constant movement
• Failed hydraulic oil temperature sensor with internal short circuit or degraded thermistor element (common after 8,000+ operating hours)
• Corroded or damaged sensor connector allowing moisture intrusion and creating high resistance or open circuits
• Chafed wiring where the harness contacts the frame, hydraulic lines, or mounting brackets—a known issue on older ZX-5A series machines
• ECM internal fault or poor ground connection at the controller (less common but possible on high-hour machines)

How to Troubleshoot and Fix Code 20107-2

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor mounted on the hydraulic tank (typically on the left side of the machine). Inspect the sensor connector for corrosion, bent pins, oil contamination, or physical damage. On used excavators, carefully trace the entire wiring harness from sensor to ECM, looking for worn insulation, rub points against metal surfaces, or previous repair attempts with electrical tape.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms (consult service manual for exact specification). Next, check for voltage supply at the harness connector—you should see approximately 5 volts on the signal wire with ignition on. A reading above 4.8 volts suggests an open circuit between sensor and ECM.

Step 3: Circuit Continuity Check With sensor disconnected and ignition off, test continuity from the sensor connector pins back to the ECM connector. Check both the signal wire and ground return path. Infinite resistance indicates a break in the wiring. Also verify the ground circuit has less than 1 ohm resistance to chassis ground—corroded grounds are extremely common on excavators operating in harsh environments.

Step 4: Component Replacement If sensor resistance is out of specification or wiring shows damage, replace the defective component using genuine Hitachi parts or quality OEM equivalents. When installing a new sensor, apply dielectric grease to connector terminals to prevent future corrosion. For used machines, consider replacing the entire harness section if multiple chafe points or aged insulation are evident—this prevents repeat failures.

Disclaimer: This guide provides general diagnostic information. Always consult the official Hitachi ZX690LCH-5A service manual for exact specifications and procedures. Complex electrical issues should be diagnosed by certified Hitachi technicians with proper diagnostic software and tools.