What is Kobelco SK350LC-8 Fault Code G042?

Kobelco SK350LC-8 Fault Code G042 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 relates to the sensor responsible for monitoring engine operating temperature and preventing overheating damage.

The coolant temperature sensor sends critical voltage signals to the ECM, which uses this data to regulate fuel injection timing, cooling fan operation, and overall engine performance. On the SK350LC-8, this sensor is vital for protecting the Hino J05E engine from thermal stress during heavy excavation operations. When this fault is active, the ECM may operate in failsafe mode using default temperature values, which can significantly reduce machine efficiency and potentially cause long-term engine damage if not addressed promptly.

Common Symptoms

When Code G042 is active on your Kobelco SK350LC-8, you may experience:

• Engine warning light illuminated on the dashboard or monitor panel
• Cooling fan running continuously at maximum speed, even during cold starts
• Reduced engine power or derate mode activation to protect the engine
• Difficulty starting or rough idle conditions, particularly when the engine is cold
• Abnormal temperature gauge readings, showing either too high or too low temperatures that don't match actual engine conditions

Potential Causes

The most common technical reasons for Code G042 on used SK350LC-8 excavators include:

• Faulty coolant temperature sensor due to internal element failure or contamination from degraded coolant
• Damaged wiring harness or corroded connector pins at the sensor plug, common in machines exposed to harsh environments
• Broken or chafed wires along the harness routing near the engine block where vibration causes rubbing
• Poor electrical ground connection at the sensor mounting point or ECM ground terminals
• ECM internal fault (rare) affecting the temperature sensor input circuit
• Low coolant level causing intermittent sensor exposure and erratic readings

How to Troubleshoot and Fix Code G042

Step 1: Visual Inspection Begin by checking the coolant level in the expansion tank and radiator. Locate the coolant temperature sensor (typically mounted on the engine block near the thermostat housing on the J05E engine). Inspect the sensor connector for corrosion, bent pins, or moisture intrusion. Check the wiring harness from sensor to ECM for visible damage, particularly where it passes near moving components or sharp edges.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms; at operating temperature (80°C/176°F), it should drop to approximately 300-400 ohms. Compare your readings against Kobelco's specifications. Also test for continuity in the wiring between the sensor and ECM connector pins, and verify less than 5 ohms resistance.

Step 3: Advanced Diagnostics Connect Kobelco diagnostic software (KOMTRAX or authorized scan tool) to read live sensor data and observe temperature values during engine warm-up. The reading should gradually increase smoothly. Erratic jumps or frozen values indicate sensor failure. Check for voltage supply at the sensor connector—should be approximately 5 volts reference voltage from the ECM.

Step 4: Component Replacement for Used Excavators For used machines, even if testing shows marginal sensor performance, replacement is often cost-effective given sensor age. When replacing, always use OEM Kobelco parts or equivalent quality sensors specified for Hino J05E engines. Clean the sensor mounting bore thoroughly and apply fresh coolant-resistant thread sealant. After installation, bleed the cooling system properly and clear codes using diagnostic software.

Critical for used excavators: Before replacing the sensor, thoroughly clean all electrical connectors with contact cleaner and apply dielectric grease to prevent future corrosion. Inspect the entire harness for wear points and secure with new zip ties away from heat sources.

---

Disclaimer: This guide provides general troubleshooting information for Kobelco SK350LC-8 Fault Code G042. Always consult your machine's official service manual and consider professional diagnostic assistance from a certified Kobelco technician for complex electrical issues or if you're uncertain about any procedure.