What is Hitachi EX200-3 Fault Code 110-3?

Fault Code 110-3 on the Hitachi EX200-3 excavator indicates an Engine Coolant Temperature Sensor Circuit Malfunction, specifically a signal voltage abnormality or intermittent open circuit condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects that the coolant temperature sensor is sending voltage readings outside the acceptable range (typically 0.2-4.8V) or experiencing circuit interruptions.

This code is critical for the EX200-3 because the coolant temperature sensor directly influences fuel injection timing, engine warm-up enrichment, and cooling fan activation. When this sensor fails or sends erratic signals, the ECM cannot properly regulate engine temperature, potentially leading to overheating, excessive fuel consumption, or cold-start difficulties. On used excavators, this sensor circuit is particularly vulnerable to corrosion and wiring degradation due to heat cycling and environmental exposure.

Common Symptoms

• Check Engine Light or Warning Lamp illuminated on the instrument cluster
• Hard starting when the engine is cold, or excessive white smoke during warm-up
• Engine overheating or cooling fan running continuously even when coolant is cold
• Rough idle or irregular engine performance, especially during initial operation
• Reduced power output or engine entering protective derate mode to prevent damage

Potential Causes

The most common technical causes for Code 110-3 on used EX200-3 excavators include:

• Faulty coolant temperature sensor with internal resistance drift (common failure after 5,000+ operating hours)
• Corroded or loose connector at the sensor harness plug near the thermostat housing
• Damaged wiring harness between the sensor and ECM, particularly at rub points near the engine mounting brackets or fuel injection pump
• Intermittent ground connection due to corroded ground terminals on the engine block
• ECM internal fault (rare, but possible on high-hour machines with moisture intrusion)
• Coolant contamination causing sensor element coating or failure

How to Troubleshoot and Fix Code 110-3

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the cylinder head near the thermostat housing. Inspect the sensor connector for corrosion, bent pins, or moisture intrusion. On used excavators, check the wiring harness for chafing against the engine block, particularly where it routes near vibration points. Clean all connector terminals with electrical contact cleaner.

Step 2: Sensor Resistance Testing Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At 20°C (68°F), resistance should read approximately 2,000-3,000 ohms; at 80°C (176°F), it should drop to 200-400 ohms. Values significantly outside this range indicate sensor failure. Compare readings against Hitachi's specifications for your specific engine serial number.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition ON (engine off), measure voltage at the harness connector from the ECM side. You should see approximately 5 volts on the signal wire. If voltage is absent, trace the harness back to the ECM for breaks or shorts. Check ground continuity (should be less than 1 ohm resistance to engine block).

Step 4: Harness and Connector Repair For used machines, carefully inspect the harness routing for wear points common to the EX200-3, especially near the fuel filter housing and hydraulic pump mount. Repair any damaged insulation with heat-shrink tubing rated for engine compartment temperatures. Apply dielectric grease to connector pins before reassembly to prevent future corrosion.

Step 5: Component Replacement and Verification If testing confirms sensor failure, replace with a genuine Hitachi or OEM-equivalent sensor (avoid low-quality aftermarket parts on used excavators, as they often fail prematurely). After installation, clear the fault code using Hitachi diagnostic software (Dr.EX) or a compatible scan tool. Run the engine through a complete heat cycle and verify the code does not return.

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Disclaimer: This guide provides general troubleshooting information for Hitachi EX200-3 excavators. Always consult the official service manual for your machine's serial number and seek assistance from a certified Hitachi technician for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.