Hitachi EX200-2 Fault Code 06: Complete Diagnostic Guide

What is Hitachi EX200-2 Fault Code 06?

Fault Code 06 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 between 0.5-4.5 volts.

This fault is critical for the EX200-2's performance because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, idle speed control, and engine protection protocols. Ignoring this code can lead to poor fuel economy, overheating, or catastrophic engine damage on these older machines.

Common Symptoms

When Code 06 is active, operators typically experience:

• Engine warning light illuminated on the instrument panel
• Hard starting or extended cranking time, especially in cold conditions
• Rough idle or unstable engine RPM during warm-up
• Black smoke from the exhaust due to improper fuel mixture
• Engine overheating without corresponding temperature gauge readings

Potential Causes

The most common technical reasons for Code 06 on used EX200-2 excavators include:

• Faulty coolant temperature sensor – Internal resistance drift is common after 5,000+ operating hours
• Damaged wiring harness – Known rub points exist near the engine mount brackets where harness insulation wears through
• Corroded electrical connectors – The sensor connector is exposed to coolant mist and develops corrosion over time
• Low coolant level – Exposes the sensor tip to air, causing erratic readings
• ECM internal fault – Rare, but possible in high-hour machines with moisture intrusion

How to Troubleshoot and Fix Code 06

Step 1: Visual Inspection Check coolant level first. Inspect the coolant temperature sensor (located on the thermostat housing) and its wiring harness for physical damage, corrosion, or oil contamination. On used excavators, pay special attention to harness routing near moving components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms. Check harness continuity from sensor connector to ECM pins and verify no shorts to ground.

Step 3: Signal Verification With the sensor connected and ignition on (engine off), measure voltage at the sensor connector. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent, trace the harness for breaks or check ECM power supply circuits.

Step 4: Component Replacement Replace the sensor if resistance values are out of specification. For used machines, always apply dielectric grease to connectors and secure harnesses away from heat sources to prevent recurrence.

---

Disclaimer: This guide provides general diagnostic information. Always consult the Hitachi service manual for your specific serial number and consider professional assistance for complex electrical diagnostics or ECM programming issues.