What is Hitachi ZX350LCK-5G Fault Code 44?

Fault Code 44 on the Hitachi ZX350LCK-5G excavator indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, typically indicating an open circuit, short circuit, or out-of-range reading.

The ECT sensor plays a critical role in engine management by monitoring coolant temperature and sending real-time data to the ECM. This information directly affects fuel injection timing, idle speed control, and engine protection systems. On used excavators like the ZX350LCK-5G, a faulty coolant temperature sensor can cause the ECM to operate in failsafe mode, resulting in reduced performance and potential engine damage if left unaddressed.

Common Symptoms

When Code 44 is active on your Hitachi ZX350LCK-5G, operators typically experience:

• Check Engine Light or Warning Lamp illuminated on the instrument cluster
• Hard starting or extended cranking time, especially in cold conditions
• Rough idle or engine running rich due to incorrect fuel mixture calculations
• Engine derating or reduced power output as the ECM enters protective mode
• Cooling fan running continuously at high speed regardless of actual engine temperature

Potential Causes

Several technical failures can trigger Code 44 on used ZX350LCK-5G excavators:

• ECT sensor failure due to internal element degradation or contamination from old coolant
• Wiring harness damage at common rub points near the engine block or frame rails
• Corroded or loose connector pins at the sensor plug, especially on machines exposed to harsh environments
• Open or short circuit in the sensor wiring between the ECT sensor and ECM
• Failed ECM (rare) with internal circuit board damage affecting the sensor input channel
• Coolant system issues causing actual overheating that damages the sensor element

How to Troubleshoot and Fix Code 44

Step 1: Visual Inspection Begin by locating the ECT sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, bent pins, or moisture intrusion. On used excavators, check the entire wiring harness from sensor to ECM for abrasion, cuts, or damage from rubbing against frame components.

Step 2: Electrical Testing Disconnect the ECT sensor connector. Using a digital multimeter, measure the sensor's resistance at various temperatures (consult Hitachi service manual for specific resistance values—typically 2,000-3,000 ohms at 68°F). Check for continuity in the wiring harness and verify supply voltage (usually 5V reference) from the ECM.

Step 3: Component Replacement If the sensor reads out-of-spec or the wiring shows open/short conditions, replace the defective component. Clean all connector terminals with electrical contact cleaner before reassembly. Clear the fault code using Hitachi diagnostic software (Dr.EX) or a compatible scan tool, then perform a test run to verify the repair.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Hitachi service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues.