Hitachi ZX110 Fault Code 04: Complete Diagnostic Guide

What is Hitachi ZX110 Fault Code 04?

Fault Code 04 on the Hitachi ZX110 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading. This code is triggered when the Engine Control Module (ECM) detects voltage signals outside the expected range from the coolant temperature sensor, typically indicating either an open circuit, short circuit, or sensor degradation.

The coolant temperature sensor is critical for the ZX110's performance because it directly influences fuel injection timing, engine warm-up cycles, and protection against overheating. When this sensor fails or provides incorrect data, the ECM may default to safe mode, limiting engine performance and potentially causing unnecessary shutdowns.

Common Symptoms

When Code 04 is active on your Hitachi ZX110, operators typically experience:

• Engine warning light illuminated on the instrument panel
• Difficulty starting the engine, especially during cold weather conditions
• Engine running rough or failing to reach optimal operating temperature
• Reduced engine power or derate mode activation to protect components
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions

Potential Causes

The most common technical causes for Code 04 on used ZX110 excavators include:

• Coolant temperature sensor failure due to age, corrosion, or internal element degradation
• Damaged or corroded wiring harness connections at the sensor plug
• Chafed wires along known rub points near the engine block or frame rails
• Poor ground connections causing voltage irregularities in the sensor circuit
• ECM internal fault (rare, but possible in high-hour machines)
• Coolant contamination causing sensor element coating or failure

How to Troubleshoot and Fix Code 04

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block (typically near the thermostat housing). Check for physical damage, coolant leaks, or corrosion on the connector. On used excavators, pay special attention to harness wear where wires contact metal surfaces.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across its terminals. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Test the wiring harness for continuity between the sensor connector and ECM pins.

Step 3: Voltage Check With the ignition on and sensor disconnected, measure reference voltage at the harness connector—should read approximately 5 volts. If voltage is absent, trace the circuit back toward the ECM for breaks or shorts.

Step 4: Component Replacement If the sensor tests outside specifications or wiring shows damage, replace the faulty component. For used machines, always apply dielectric grease to connectors to prevent future corrosion. Clear the code using Hitachi diagnostic software or a compatible scan tool and verify repair.

---

Disclaimer: This guide provides general diagnostic information. Always consult your Hitachi service manual and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with excavator systems.