Kobelco SK200-6 Fault Code G-3: Complete Diagnostic Guide

What is Kobelco SK200-6 Fault Code G-3?

Fault Code G-3 indicates a malfunction in the engine overheat warning system, specifically a failure in the coolant temperature sensor circuit or an actual engine overheating condition. This code is triggered when the Engine Control Module (ECM) detects abnormal signals from the water temperature sensor or when coolant temperatures exceed safe operating parameters (typically above 105-110°C).

For the SK200-6 model equipped with Hino or Isuzu engines, this code is critical because prolonged overheating can cause catastrophic damage to cylinder heads, gaskets, and the engine block itself. The ECM may initiate derate mode, reducing engine power to prevent thermal damage, which severely impacts productivity on job sites.

Common Symptoms

When Code G-3 is active, operators typically experience:

• Engine overheat warning lamp illuminated continuously on the instrument panel
• Audible alarm sounding in the cab, alerting the operator to temperature issues
• Reduced engine power or automatic shutdown in severe cases to protect internal components
• Erratic temperature gauge readings that fluctuate abnormally or show maximum temperature immediately after startup
• Steam or coolant vapor visible from the engine compartment in actual overheat conditions

Potential Causes

The most common technical causes for Code G-3 on used SK200-6 excavators include:

• Faulty coolant temperature sensor – age-related sensor degradation or internal circuit failure
• Damaged wiring harness – particularly at harness rub points near the engine mount or cylinder head where vibration causes wire insulation breakdown
• Corroded or loose electrical connectors at the temperature sensor plug (common in machines exposed to harsh environments)
• Low coolant levels due to leaks in radiator, hoses, or water pump seals
• Blocked radiator core restricting airflow and causing genuine overheating
• Faulty thermostat stuck closed, preventing proper coolant circulation
• ECM calibration issues or internal ECM fault (less common)

How to Troubleshoot and Fix Code G-3

Step 1: Visual Inspection Begin by checking coolant levels in the radiator and overflow tank with the engine cold. Inspect all hoses, clamps, and the radiator for visible leaks or damage. On used excavators, pay special attention to harness routing near the engine – look for worn insulation or wires contacting hot surfaces.

Step 2: Test the Coolant Temperature Sensor Locate the water temperature sensor (typically mounted on the cylinder head or thermostat housing). Disconnect the electrical connector and inspect for corrosion, moisture, or bent pins. Using a digital multimeter, measure sensor resistance – it should read approximately 2-3 kΩ at 20°C (refer to Kobelco service manual for exact specifications). Test harness continuity from the sensor connector back to the ECM.

Step 3: Check for Actual Overheating Start the engine and monitor coolant temperature with an infrared thermometer while comparing readings to the instrument panel gauge. Verify the cooling fan engages properly and check thermostat operation by feeling upper and lower radiator hoses for temperature equalization. If actual overheating exists, address cooling system issues before replacing sensors.

Step 4: Clear Code and Monitor After repairs, use Kobelco diagnostic software or a compatible scan tool to clear the fault code. Operate the machine under normal load conditions and monitor for code recurrence. For used machines, replace the temperature sensor preemptively if it's original equipment, as sensor failure rates increase significantly after 5,000+ operating hours.

Disclaimer: This guide provides general troubleshooting procedures. Always consult the official Kobelco service manual for your specific machine serial number and seek assistance from certified technicians for complex repairs involving the ECM or engine internals.