What is Kobelco SK75-8 Fault Code B013?

Fault Code B013 on the Kobelco SK75-8 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an implausible signal from the coolant temperature sensor, which may include voltage readings outside normal parameters (typically 0.5-4.5V) or a sensor output that doesn't correlate with actual engine operating conditions.

This code is critical for the SK75-8's performance because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, manage engine protection protocols, and control the cooling fan operation. Ignoring this fault can lead to engine overheating, reduced power output, or premature component wear—especially problematic in used machines where cooling system degradation may already be present.

Common Symptoms

• Engine warning light illuminated on the operator display panel
• Reduced engine power or activation of derate mode to protect the engine from thermal damage
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Hard starting or rough idle, particularly when the engine is cold
• Black smoke from exhaust due to improper fuel-air mixture caused by incorrect temperature compensation

Potential Causes

The most common technical reasons for Code B013 on used SK75-8 excavators include:

• Faulty coolant temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Damaged or corroded wiring harness between the sensor and ECM, particularly at connector points near the engine block where vibration and heat cycles cause wear
• Corroded or loose electrical connectors at the sensor or ECM—moisture intrusion is frequent in used machines
• Low coolant level or air pockets in the cooling system causing inaccurate temperature readings
• ECM internal fault or software calibration issue (less common but possible in older units)
• Shorted or open circuit in the sensor signal wire, often from harness rubbing against engine components

How to Troubleshoot and Fix Code B013

Step 1: Visual Inspection Begin by checking coolant level in the radiator and expansion tank. Inspect the coolant temperature sensor (typically located on the cylinder head or thermostat housing) and its wiring harness for obvious damage, corrosion, or oil contamination. On used excavators, pay special attention to connector pins—clean with electrical contact cleaner if corrosion is present.

Step 2: Electrical Testing Using a digital multimeter, disconnect the coolant temperature sensor connector and measure resistance across the sensor terminals. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult Kobelco service manual for exact specifications). Test the wiring harness continuity from sensor to ECM and check for shorts to ground. Verify reference voltage from the ECM (should be approximately 5V).

Step 3: Component Replacement and Verification If the sensor resistance is out of specification or the wiring shows damage, replace the faulty component. For used machines, consider replacing both the sensor and connector pigtail simultaneously, as connector corrosion often recurs. After replacement, clear the fault code using Kobelco diagnostic software or a compatible scan tool, then operate the machine through a full heat cycle to verify the repair.

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