Hitachi ZX200LC-5G Fault Code 16605-2: Complete Diagnostic Guide

What is Hitachi ZX200LC-5G Fault Code 16605-2?

Fault Code 16605-2 indicates a Low Signal Voltage condition in the Engine Coolant Temperature (ECT) Sensor Circuit on the Hitachi ZX200LC-5G excavator. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects a voltage reading below the manufacturer's specified threshold, typically under 0.2 volts, from the coolant temperature sensor circuit.

The ECT sensor plays a critical role in engine performance management on the Isuzu engine powering this excavator. It provides real-time coolant temperature data that the ECM uses to adjust fuel injection timing, idle speed, and emission controls. When this circuit fails, the ECM cannot accurately monitor engine temperature, potentially leading to improper fuel mixture, starting difficulties, and increased engine wear—particularly problematic in used machines with accumulated operating hours.

Common Symptoms

• Check Engine Light illuminated on the instrument panel with possible overheat warning icon
• Hard starting conditions, especially during cold weather, as the ECM defaults to a fixed temperature value
• Rough idle or hunting RPM as the engine management system struggles with incorrect temperature data
• Black smoke from exhaust due to overly rich fuel mixture from faulty temperature compensation
• Reduced engine power or derate mode activation if the ECM detects prolonged sensor malfunction

Potential Causes

The most common technical failures causing Code 16605-2 on used ZX200LC-5G excavators include:

• Open circuit in ECT sensor wiring harness, particularly at known rub points near the engine mounting brackets and behind the fuel filter assembly
• Corroded or loose connector terminals at the sensor or ECM connection points—extremely common on machines operating in wet or coastal environments
• Failed ECT sensor with internal open circuit, typically after 5,000+ operating hours
• Damaged wiring insulation from rodent activity or harness chafing against the engine block
• ECM internal circuit failure (rare, but possible on high-hour machines with electrical system history)

How to Troubleshoot and Fix Code 16605-2

Step 1: Visual Inspection Begin with a thorough physical examination of the ECT sensor located on the engine coolant outlet housing (driver's side of engine block). Inspect the two-wire connector for corrosion, moisture intrusion, or bent pins. On used excavators, carefully check the entire wiring harness routing from sensor to ECM for obvious damage, particularly where the harness contacts metal surfaces or passes through grommets.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the ECT sensor connector and measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,300-2,700 ohms. Compare readings against the Hitachi specification chart for your engine serial number. Next, check for continuity in both wires from the sensor connector back to the ECM connector pins (typically E2-17 and E2-35 on the 134-pin connector). Resistance should be less than 5 ohms per wire.

Step 3: Voltage Supply Check With the ignition on and sensor disconnected, measure reference voltage at the harness-side connector. You should see approximately 5.0 volts on the signal wire. If voltage is absent or incorrect, trace the circuit toward the ECM, checking for damaged wiring or poor ground connections at G101 (frame ground near battery box).

Step 4: Component Replacement and Verification If the sensor tests faulty, replace with a genuine Hitachi/Isuzu ECT sensor (part number 8-97328-117-1 or equivalent). For used machines, always apply dielectric grease to connector terminals before reconnection to prevent future corrosion. After replacement, clear the fault code using Hitachi Dr.EX diagnostic software or a compatible scan tool, then operate the machine through a full heat cycle to verify proper operation.

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Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the official Hitachi service manual for your specific machine serial number and seek professional assistance if you're unfamiliar with electrical diagnostics or lack proper testing equipment. Improper repairs may cause additional damage or safety hazards.