What is Kobelco SK135SRLC-2 Fault Code D013?

Fault Code D013 on the Kobelco SK135SRLC-2 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 indicating an open circuit, short circuit, or sensor degradation.

The coolant temperature sensor is critical for this Kobelco excavator's performance because it directly influences fuel injection timing, engine warm-up cycles, and protection against overheating. When the ECM cannot accurately read engine temperature, it defaults to preset values that may cause inefficient combustion, increased emissions, and potential engine protection mode activation. For used machines like the SK135SRLC-2, this sensor and its wiring harness are particularly vulnerable to age-related deterioration, making D013 a relatively common issue in higher-hour units.

Common Symptoms

When Code D013 is active on your Kobelco SK135SRLC-2, you may experience:

• Check engine light or malfunction indicator lamp illuminated on the instrument panel
• Hard starting or extended cranking time, especially during cold weather conditions
• Rough idle or erratic engine RPM fluctuations during warm-up phase
• Engine derate mode activation, limiting maximum power output to protect components
• Black smoke from exhaust due to improper fuel-to-air ratio compensation

Potential Causes

The most common technical reasons for D013 appearing on used SK135SRLC-2 excavators include:

• Failed coolant temperature sensor due to internal resistance drift or element failure (common after 5,000+ operating hours)
• Damaged wiring harness near the engine block where vibration and heat cause insulation breakdown
• Corroded or loose electrical connectors at the sensor or ECM, especially in machines exposed to moisture or harsh environments
• Broken or frayed wires at known rub points between the engine and chassis harness routing
• ECM internal fault (rare, but possible in older units with moisture intrusion)
• Coolant contamination on sensor terminals causing erratic resistance readings

How to Troubleshoot and Fix Code D013

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, bent pins, or coolant residue. Check the wiring harness from the sensor back to the ECM for visible damage, especially at mounting brackets and areas where the harness contacts metal surfaces—a common wear point on used excavators.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at various temperatures. At 68°F (20°C), resistance should typically read between 2,000-3,000 ohms (consult Kobelco specifications for exact values). Perform a voltage check at the harness connector with the sensor disconnected—you should see approximately 5 volts reference voltage from the ECM. If voltage is absent, trace the harness for breaks.

Step 3: Circuit Continuity and Repair Test continuity from the sensor connector pins back to the ECM connector using your multimeter. Any reading above 5 ohms indicates excessive resistance from corroded connections or damaged wiring. For used machines, pay special attention to harness rub-through points near engine mounts. If the sensor tests within specifications but wiring shows degradation, repair or replace the affected harness section rather than defaulting to sensor replacement.

Step 4: Component Replacement If testing confirms a faulty sensor, replace it with a genuine Kobelco or OEM-equivalent part and apply anti-seize compound to threads. After installation, clear the fault code using diagnostic software (Kobelco-specific scanner recommended) and verify the code does not return after running the engine through a complete heat cycle.

Disclaimer: This guide provides general troubleshooting information for Code D013. Always consult the official Kobelco service manual for your specific serial number and consider professional diagnosis if you lack appropriate diagnostic tools or experience with heavy equipment electrical systems.