What is Hitachi ZX870-5A (HCMC) Fault Code 14106-2?

Fault Code 14106-2 indicates a hydraulic oil temperature sensor circuit malfunction in the Hitachi ZX870-5A excavator. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, specifically indicating a voltage reading that is too high or an open circuit condition.

This code directly affects the machine's ability to monitor and regulate hydraulic system temperature, which is critical for the ZX870-5A's operational safety and efficiency. The hydraulic oil temperature sensor provides real-time data to the ECM, allowing the system to prevent overheating damage to pumps, motors, and seals. When this sensor fails or provides incorrect readings, the excavator may enter derate mode or display false temperature warnings, significantly impacting productivity on job sites.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the instrument cluster, even when oil feels cool to touch
• Machine enters reduced power mode (derate) to protect hydraulic components from perceived overheating
• Erratic temperature gauge readings that fluctuate abnormally or display maximum temperature immediately upon startup
• ECM error messages displayed on the monitor panel indicating sensor malfunction
• Intermittent loss of hydraulic function or reduced flow rates as the system attempts protective measures

Potential Causes

The most common causes of Code 14106-2 on used ZX870-5A excavators include:

• Damaged or corroded wiring harness near the hydraulic tank where the sensor connects—this area is particularly vulnerable to hydraulic fluid contamination and vibration wear
• Failed hydraulic oil temperature sensor due to internal resistance drift or element breakage (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor plug, especially on machines operated in coastal or high-humidity environments
• Chafed wiring at known rub points near the swing bearing or along the main chassis harness routing
• ECM internal fault (rare) affecting the sensor input circuit
• Aftermarket sensor incompatibility if previous repairs used non-OEM replacement parts

How to Troubleshoot and Fix Code 14106-2

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor on the hydraulic tank (typically mounted on the left side of the tank). Inspect the wiring harness from the sensor to the main harness connector for visible damage, oil contamination, chafing, or burnt insulation. On used excavators, pay special attention to areas where the harness passes near moving components or sharp edges.

Step 2: Connector and Resistance Testing Disconnect the sensor connector and inspect for corrosion, bent pins, or moisture intrusion. Using a digital multimeter, measure the sensor's resistance across its terminals. A properly functioning Hitachi hydraulic temperature sensor typically shows 200-400 ohms at room temperature (refer to service manual for exact specifications). An open circuit (infinite resistance) or short circuit (near-zero resistance) confirms sensor failure.

Step 3: Wiring Continuity Check With the sensor disconnected, check continuity and resistance from the sensor connector back to the ECM connector using wiring diagrams. Measure for shorts to ground or opens in the circuit. For used machines, flex the harness while testing to identify intermittent breaks caused by internal wire fractures.

Step 4: Voltage Signal Verification Reconnect the sensor and use Hitachi Dr. EX diagnostic software or a compatible scan tool to monitor live sensor voltage. The ECM typically supplies 5-volt reference voltage to the sensor. Readings consistently at or near 5 volts indicate an open circuit; 0 volts suggests a short to ground.

Step 5: Component Replacement If testing confirms sensor failure, replace with genuine Hitachi parts (Part Number varies by serial number range). Clean all connector terminals with electrical contact cleaner and apply dielectric grease before reconnection. Clear the fault code and perform a system test cycle, monitoring temperature readings during warm-up.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Hitachi service manual for your specific machine serial number and seek professional diagnostic assistance when dealing with complex electrical systems. Improper repairs may void warranties or create safety hazards.