What is Hitachi ZX330LC-5G Fault Code 16605-2?

Fault Code 16605-2 indicates a malfunction in the Engine Coolant Temperature (ECT) sensor circuit, specifically registering an intermittent or erratic voltage signal outside the normal operating range. This code is triggered when the Engine Control Module (ECM) detects inconsistent data from the coolant temperature sensor, which monitors the engine's thermal status and directly affects fuel injection timing, idle speed, and engine protection protocols.

For the Hitachi ZX330LC-5G equipped with an Isuzu engine, this code is critical because the ECM relies on accurate coolant temperature readings to prevent overheating and optimize combustion efficiency. An unreliable ECT sensor signal can cause the engine to run in a protective derate mode or trigger unnecessary shutdowns, significantly impacting productivity on job sites.

Common Symptoms

• Check Engine Light or warning lamp illuminated on the instrument cluster
• Engine running in cold start mode continuously, resulting in rough idling or excessive fuel consumption
• Intermittent engine power derate or reduced hydraulic response during operation
• Engine fan running at maximum speed constantly, even when coolant temperature is normal
• Difficulty starting the engine when warm, or extended cranking times

Potential Causes

The most common causes of fault code 16605-2 on used Hitachi ZX330LC-5G excavators include:

• Corroded or loose connector pins at the ECT sensor harness (common wear point due to engine vibration and heat cycles)
• Damaged or frayed wiring along the harness routing near the engine block, especially where the harness contacts metal surfaces
• Failed ECT sensor due to internal element degradation or contamination from coolant additives in older machines
• Intermittent ground circuit failure affecting sensor voltage reference
• ECM internal fault (rare, but possible in high-hour machines with moisture intrusion history)

How to Troubleshoot and Fix Code 16605-2

Step 1: Visual Inspection Begin by inspecting the ECT sensor connector located on the engine's coolant outlet housing. Check for corrosion, moisture, or damaged pins. On used excavators, this connector often shows green corrosion buildup—clean with electrical contact cleaner and ensure the seal and locking tab are intact.

Step 2: Sensor and Circuit Testing Using a digital multimeter, measure the ECT sensor resistance with the engine cold (should typically read 2,000-3,000 ohms at 20°C). Compare readings against Hitachi specifications. Next, backprobe the sensor connector and check for 5-volt reference signal from the ECM with the ignition on. Verify ground circuit continuity (should be less than 1 ohm resistance to chassis ground).

Step 3: Harness and Wiring Inspection Trace the sensor harness from the ECT sensor back to the ECM, checking for abrasion points, especially where the harness passes near exhaust components or sharp metal edges. On older ZX330LC-5G models, the harness routing near the fuel filter housing is a known rub point—inspect carefully and repair any exposed wires with heat-shrink tubing and protective loom.

Step 4: Component Replacement If testing confirms sensor failure, replace the ECT sensor with a genuine Hitachi or OEM-equivalent part. After replacement, clear the fault code using Hitachi diagnostic software (Dr.EX) or a compatible J1939 scan tool, then monitor for code recurrence during a full heat cycle.

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Disclaimer: This guide provides general troubleshooting information. Always consult the Hitachi ZX330LC-5G service manual and consider professional diagnostic assistance for complex electrical issues or if you lack experience with heavy equipment systems.