What is Kobelco SK135SRLC-2 Fault Code C024?

Kobelco SK135SRLC-2 fault code C024 indicates a malfunction in the engine coolant temperature sensor circuit or an out-of-range temperature reading detected by the ECM (Engine Control Module). This code specifically points to either a sensor failure, wiring issue, or coolant system problem that prevents the ECM from accurately monitoring engine operating temperature.

The coolant temperature sensor plays a critical role in the SK135SRLC-2's engine management system. It provides real-time temperature data that the ECM uses to adjust fuel injection timing, throttle response, and activate cooling fan cycles. When this sensor circuit fails, the engine cannot optimize performance or protect itself from overheating, potentially leading to severe engine damage on used excavators where cooling systems may already be compromised.

Common Symptoms

• Check engine light or malfunction indicator lamp illuminated on the instrument panel
• Engine derate mode activated, resulting in reduced power output and limited RPM range
• Hard starting or rough idle, especially during cold starts when temperature compensation is critical
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Erratic temperature gauge readings or gauge stuck in one position

Potential Causes

The most common causes of code C024 on used SK135SRLC-2 excavators include:

• Failed coolant temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Damaged wiring harness near the sensor connector, particularly where the harness contacts the engine block or frame rails—a known wear point on this model
• Corroded or loose electrical connectors at the sensor or ECM, especially in machines operated in wet or coastal environments
• Low coolant level or air pockets in the cooling system causing inaccurate sensor readings
• ECM internal fault affecting the sensor signal processing circuit (rare but possible in older units)
• Contaminated coolant causing sensor coating or reduced thermal conductivity

How to Troubleshoot and Fix Code C024

Step 1: Visual Inspection Check coolant level in the radiator and overflow tank. Inspect the temperature sensor (located on the engine block near the thermostat housing) and its connector for physical damage, corrosion, or coolant leaks. On used excavators, pay special attention to harness routing for abrasion points.

Step 2: Electrical Testing Using a digital multimeter, check sensor resistance at various temperatures. A typical sensor should read approximately 2,500-3,000 ohms at 68°F (20°C). Verify the ECM reference voltage at the sensor connector (typically 5 volts) with the key on, engine off.

Step 3: Harness and Ground Verification Inspect the wiring harness from sensor to ECM for continuity and shorts to ground. Check engine ground connections for tightness and corrosion. Common ground failure points include chassis ground straps behind the cab mounting area.

Step 4: Component Replacement If sensor resistance is out of specification or the connector shows corrosion, replace the coolant temperature sensor with an OEM or quality aftermarket unit. Always use fresh dielectric grease on connectors during reassembly to prevent future corrosion.

Step 5: System Reset and Verification Clear fault codes using Kobelco diagnostic software or compatible scan tool. Run the engine through normal temperature cycles and monitor for code recurrence.

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.