What is Kobelco SK130-8 Fault Code 6771?

Fault Code 6771 on the Kobelco SK130-8 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the Engine Control Module (ECM). This code specifically refers to the ECM receiving voltage signals outside the expected range from the coolant temperature sensor, which monitors engine operating temperature to optimize fuel injection, timing, and emission controls.

This fault is critical for the SK130-8's Hino diesel engine performance because the ECM relies on accurate temperature data to prevent overheating, adjust fuel delivery, and manage the diesel particulate filter (DPF) regeneration cycles. When this sensor circuit fails, the engine may enter limp mode or experience reduced power output to protect internal components from thermal damage.

Common Symptoms

When Code 6771 is active on your Kobelco SK130-8, operators typically experience:

• Engine warning light illuminated on the instrument cluster, often accompanied by a temperature warning symbol
• Reduced engine power or derate mode, limiting maximum RPM and hydraulic performance
• Difficulty starting when the engine is cold, as the ECM cannot properly adjust cold-start fuel enrichment
• Cooling fan running continuously at high speed, even when engine temperature appears normal
• Erratic temperature gauge readings on the dashboard, showing inconsistent or frozen temperature displays

Potential Causes

The most common technical failures triggering Code 6771 in used SK130-8 excavators include:

• Faulty coolant temperature sensor due to age-related degradation or internal resistance drift (typical failure point after 4,000-6,000 operating hours)
• Damaged or corroded wiring harness between the sensor and ECM, especially at connector pins exposed to coolant vapor or moisture
• Broken or chafed sensor wiring where the harness passes near the engine block or hydraulic lines (known wear point on SK130-8 models)
• Poor electrical ground connection at the sensor mounting location or ECM grounding points
• ECM software corruption or internal ECM failure (less common, but documented in earlier production SK130-8 units)
• Actual engine overheating condition causing legitimate high-temperature readings that trigger the fault code

How to Troubleshoot and Fix Code 6771

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check for visible coolant leaks, corrosion on the electrical connector, or damaged wiring. On used excavators, pay particular attention to harness routing where cables may rub against metal surfaces or hot engine components.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. A functional sensor typically shows 2,000-3,000 ohms at room temperature (consult Kobelco specifications for exact values). Check wiring continuity from sensor to ECM connector pins, and verify less than 5 ohms resistance. Inspect for voltage drop by measuring with the ignition on—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Component Replacement and Verification If resistance values are out of specification or wiring shows damage, replace the coolant temperature sensor (Kobelco part number varies by engine serial number). For used machines, always apply dielectric grease to connector pins before reassembly to prevent future corrosion. Clear the fault code using Kobelco diagnostic software or a compatible scanner, then run the engine through normal operating temperature cycles to verify the repair.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual for your specific machine serial number and consider professional diagnostic services for complex electrical issues or if you lack proper testing equipment.