Hitachi EX220-5 Fault Code 06: Complete Diagnostic Guide

What is Hitachi EX220-5 Fault Code 06?

Fault Code 06 on the Hitachi EX220-5 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading. This code is triggered when the Engine Control Module (ECM) detects voltage signals outside the normal operating range from the coolant temperature sensor, typically between 0.5-4.5 volts.

The coolant temperature sensor is critical for the EX220-5's Isuzu 6BG1T engine management system. It directly influences fuel injection timing, idle speed control, and engine protection protocols. When this sensor fails or provides incorrect data, the ECM cannot properly regulate engine performance, potentially leading to overheating, poor fuel economy, or engine damage.

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 running hotter than normal or cooling fan running continuously
• Reduced engine power or performance under load

Potential Causes

The most common technical reasons for Code 06 on used EX220-5 excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal short circuits
• Damaged or corroded wiring harness connections at the sensor plug (common wear point near the thermostat housing)
• Broken or frayed wires in the sensor circuit caused by engine vibration or heat exposure
• Corroded ECM connector pins (particularly in machines operated in wet or marine environments)
• Low coolant level causing sensor exposure and false readings
• Failed ECM (rare, but possible in high-hour machines)

How to Troubleshoot and Fix Code 06

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor location on the engine block near the thermostat housing. Check for physical damage, coolant leaks, and verify proper coolant level. Examine the sensor connector for corrosion, bent pins, or moisture intrusion—common issues on used excavators.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to measure resistance. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms. Test the wiring harness for continuity between the sensor connector and ECM pins. Check for shorts to ground using the ohmmeter function.

Step 3: Voltage Check With the ignition on and sensor disconnected, measure voltage at the harness connector. You should see approximately 5 volts reference voltage from the ECM. No voltage indicates a wiring issue or ECM problem.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Hitachi or OEM-equivalent part. For used excavators, always apply dielectric grease to connector pins to prevent future corrosion. Clear the fault code using Hitachi diagnostic software (Dr.EX) or by disconnecting the battery for 30 minutes.

Disclaimer: This guide provides general diagnostic information. Always consult the official Hitachi service manual and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.