Hitachi EX200-2 Fault Code 19: Complete Diagnostic Guide

What is Hitachi EX200-2 Fault Code 19?

Fault Code 19 on the Hitachi EX200-2 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading. This code is triggered when the Electronic Control Module (ECM) detects voltage signals outside the normal operating range from the coolant temperature sensor, typically indicating an open circuit, short circuit, or sensor failure.

This fault is critical for the EX200-2's performance because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, engine warm-up cycles, and prevent overheating damage. Ignoring this code can lead to poor fuel economy, increased emissions, and potential engine damage from inadequate temperature monitoring.

Common Symptoms

When Code 19 is active, operators typically experience:

• Temperature gauge reading abnormally high, low, or erratic on the instrument panel
• Warning lights illuminated on the dashboard, particularly the coolant temperature warning
• Difficulty starting the engine, especially in cold conditions due to improper fuel enrichment
• Engine running rough during warm-up or failing to reach optimal operating temperature
• Reduced engine power or derate mode activation as a protective measure

Potential Causes

The most common technical causes for Code 19 on used EX200-2 excavators include:

• Coolant temperature sensor failure due to age, corrosion, or internal element degradation
• Damaged or corroded wiring harness connections at the sensor plug (common rub point near engine block)
• Broken or frayed wires in the sensor circuit, particularly where the harness routes over the engine
• Corroded or loose ground connections affecting sensor signal integrity
• ECM internal fault (rare, but possible in high-hour machines)
• Contaminated coolant causing sensor element fouling or coating

How to Troubleshoot and Fix Code 19

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 pins. On used excavators, examine the entire wiring harness for wear points, especially where it contacts the engine or frame.

Step 2: Electrical Testing Disconnect the sensor and use a multimeter to measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms (consult service manual for exact specifications). Test the harness for continuity to the ECM and check for shorts to ground.

Step 3: Signal Verification With the sensor connected and engine cold, use Hitachi diagnostic software or a compatible scan tool to monitor live coolant temperature data. Compare readings against actual engine temperature. Replace the sensor if readings are implausible or frozen.

Step 4: Harness and Ground Repair For used machines, thoroughly clean all connector terminals with electrical contact cleaner and apply dielectric grease. Verify ground circuit integrity, as corrosion at ground points is extremely common on older excavators.

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