Hitachi ZX110-E Fault Code 04: Complete Diagnostic Guide

What is Hitachi ZX110-E Fault Code 04?

Fault Code 04 on the Hitachi ZX110-E indicates an Engine Coolant Temperature (ECT) Sensor circuit malfunction. This code is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal—either too high or too low—from the coolant temperature sensor circuit.

The ECT sensor is a thermistor-based component that monitors engine coolant temperature and sends corresponding voltage signals to the ECM. This data is critical for proper fuel injection timing, cold-start enrichment, and cooling fan activation.

On the ZX110-E's Isuzu 4HK1X engine, accurate coolant temperature readings are essential for maintaining optimal combustion efficiency and preventing thermal damage. When this circuit fails, the ECM defaults to a predetermined temperature value, potentially causing poor fuel economy and increased emissions.

Common Symptoms

• Check Engine warning light illuminated on the monitor panel
• Engine running rough during cold starts or warm-up periods
• Decreased fuel efficiency and sluggish throttle response
• Cooling fan running continuously or not engaging at all
• Derate mode activation in severe cases, limiting engine power

Potential Causes

The most frequent causes of Code 04 on used ZX110-E excavators include:

• ECT sensor failure due to age or thermal cycling degradation
• Wiring harness damage—particularly near the exhaust manifold where heat exposure causes insulation breakdown
• Corroded connector pins at the sensor or ECM junction, common in machines with high operating hours
• Open or short circuits in the sensor signal wire, often from harness chafing against frame components
• Faulty ECM ground connection causing erratic voltage readings

How to Troubleshoot and Fix Code 04

Step 1: Visual Inspection Locate the ECT sensor on the engine's thermostat housing. Inspect the wiring harness for visible damage, melting, or abrasion. On used excavators, pay particular attention to areas where wires contact metal brackets or hot components. Check connector pins for corrosion, green oxidation, or bent terminals.

Step 2: Electrical Testing Using a digital multimeter, measure the sensor's resistance. At 20°C (68°F), expect approximately 2.0-3.0 kΩ; at 80°C (176°F), expect 0.3-0.4 kΩ. Verify the 5V reference voltage at the connector with the key on. Check continuity between the sensor connector and ECM terminals.

Step 3: Component Replacement If resistance values fall outside specifications, replace the ECT sensor. Before installing new parts on used equipment, thoroughly clean connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Clear the fault code using Hitachi Dr. ZX diagnostic software and verify repair by monitoring live data.

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Disclaimer: This guide is for informational purposes only. Always consult qualified heavy diesel technicians and refer to official Hitachi service manuals for your specific machine's serial number range before performing repairs.