What is Hitachi ZX870-5A Fault Code 14104-2?

Fault Code 14104-2 indicates a malfunction in the engine coolant temperature sensor circuit, specifically a voltage signal that is too high or an open circuit condition. This code is triggered when the Engine Control Module (ECM) detects abnormal resistance or voltage readings from the coolant temperature sensor, which monitors the operating temperature of the Isuzu engine in the ZX870-5A excavator.

This fault is critical because the coolant temperature sensor provides essential data to the ECM for proper fuel injection timing, idle speed control, and engine protection protocols. When this sensor circuit fails, the ECM cannot accurately manage engine performance, potentially leading to inefficient combustion, increased emissions, and risk of engine damage from overheating conditions.

Common Symptoms

• Engine warning light or malfunction indicator illuminated on the operator display panel
• Hard starting or rough idle, especially during cold starts when the ECM relies heavily on temperature data
• Engine derate mode activated, limiting power output to protect the engine from potential damage
• Poor fuel economy and black smoke from exhaust due to incorrect fuel-air mixture calculations
• Cooling fan running continuously at high speed as the ECM defaults to maximum cooling protection mode

Potential Causes

The most common technical failures triggering Code 14104-2 on used ZX870-5A excavators include:

• Damaged or corroded wiring harness at connector points, particularly where the harness routes near the engine block and experiences heat cycling
• Failed coolant temperature sensor due to internal element deterioration or thermal stress fractures
• Open circuit caused by broken wires inside the insulation, common at harness flex points near the engine mount
• Corroded connector terminals at the sensor plug or ECM connection, especially in machines operating in humid or marine environments
• ECM internal fault affecting the sensor input circuit (rare but possible in high-hour machines)

How to Troubleshoot and Fix Code 14104-2

Step 1: Visual Inspection Inspect the coolant temperature sensor and its wiring harness for obvious damage, corrosion, or oil contamination. On used excavators, pay special attention to harness routing where it contacts hot engine surfaces or rubs against mounting brackets. Check connector terminals for green corrosion or bent pins.

Step 2: Sensor Resistance Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At 20°C (68°F), resistance should typically read 2,000-3,000 ohms (consult Hitachi service manual for exact specifications). Compare readings at different temperatures using a temperature gun to verify the sensor's thermistor response curve.

Step 3: Circuit Voltage and Continuity Check With the sensor disconnected, measure voltage at the harness connector. You should see approximately 5 volts reference voltage from the ECM. Test continuity between the sensor connector and ECM pins using wiring diagrams. Any reading above 10 ohms indicates excessive resistance from corrosion or wire damage.

Step 4: Connector and Harness Repair For used machinery, thoroughly clean all connector terminals with electrical contact cleaner and apply dielectric grease. Repair any damaged harness sections with proper gauge wire and heat-shrink tubing, ensuring routing avoids heat and abrasion points.

Step 5: Component Replacement Replace the coolant temperature sensor with a genuine Hitachi or OEM-equivalent part. After installation, clear the fault code using Dr.EX diagnostic software or compatible scan tool and perform a test run to verify proper operation.

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