What is Kobelco SK135SR-2 Fault Code D063?

Fault Code D063 on the Kobelco SK135SR-2 excavator indicates a malfunction in the engine coolant temperature sensor circuit. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, typically due to an open circuit, short circuit, or sensor failure. The coolant temperature sensor is a critical component that monitors engine operating temperature and sends real-time data to the ECM to optimize fuel injection timing, idle speed, and engine protection protocols.

For the Kobelco SK135SR-2's Hino diesel engine, proper coolant temperature monitoring is essential for preventing overheating, ensuring efficient combustion, and protecting the cylinder head and engine block from thermal damage. When this sensor circuit fails, the ECM may default to a predetermined temperature value, potentially causing poor fuel economy, rough idling, or premature engine wear on used machines already experiencing age-related degradation.

Common Symptoms

• Check engine light or malfunction indicator lamp illuminated on the instrument panel
• Engine running cooler or hotter than normal operating temperature (typically 180-200°F)
• Difficulty starting when the engine is cold, or extended cranking times
• Rough idle, particularly during warm-up phases
• Black smoke from the exhaust due to incorrect fuel mixture adjustments
• ECM entering limp mode or derate, limiting engine power to prevent potential damage

Potential Causes

The D063 code on used SK135SR-2 excavators commonly stems from age-related electrical and mechanical failures:

• Coolant temperature sensor internal failure or drift due to prolonged exposure to heat cycles
• Corroded or damaged sensor connector pins from moisture intrusion or vibration
• Broken or frayed wiring harness between the sensor and ECM, especially at common rub points near the engine mount brackets or frame rails
• Poor ground connection at the sensor mounting point caused by corrosion buildup
• ECM internal fault (rare, but possible in high-hour machines)
• Aftermarket sensor incompatibility or incorrect sensor installation during previous repairs

How to Troubleshoot and Fix Code D063

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the sensor body for physical damage, coolant leaks, or corrosion. Examine the wiring harness from the sensor to the ECM, checking for abraded insulation, broken wires, or damaged connectors—pay special attention to areas where the harness contacts metal edges or moving components.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F), resistance should typically read between 2,000-3,000 ohms (consult the Kobelco service manual for exact specifications). Test the wiring harness for continuity between the sensor connector and ECM pins, and check for shorts to ground. Measure the reference voltage from the ECM (usually 5 volts) at the disconnected harness connector.

Step 3: Component Replacement and Verification If resistance values are out of specification or wiring shows faults, replace the defective component. For used excavators, always clean connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. After repairs, clear the fault code using Kobelco diagnostic software or a compatible OBD scanner, then monitor the system during operation to confirm the repair. Run the engine through complete heat cycles to verify proper sensor function.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with excavator systems.