What is Kobelco SK250-6E Fault Code C-2?

Fault Code C-2 on the Kobelco SK250-6E indicates a malfunction in the engine cooling system's water temperature sensor circuit. Specifically, this code triggers when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, either reading excessively high (open circuit) or abnormally low (short circuit) compared to factory-specified parameters.

This fault is critical for the SK250-6E because the ECM relies on accurate coolant temperature data to manage fuel injection timing, idle speed adjustments, and engine protection protocols. When this sensor circuit fails, the excavator may enter a protective derate mode to prevent catastrophic overheating damage to the Hino J05E engine commonly found in this model. Ignoring C-2 can lead to poor fuel economy, excessive emissions, and potential engine seizure on used machines already experiencing wear.

Common Symptoms

• Engine warning light illuminated on the instrument panel, often accompanied by audible alarm
• Engine running in limp mode with reduced hydraulic power and slower cycle times
• Erratic temperature gauge readings or gauge stuck at cold/hot positions
• Difficulty starting when the engine is cold, or rough idle during warm-up
• Increased black smoke from exhaust due to improper fuel mixture compensation

Potential Causes

The most common causes of Code C-2 on used SK250-6E excavators include:

• Faulty coolant temperature sensor due to internal resistance drift (common failure point after 5,000+ hours)
• Damaged or corroded wiring harness between the sensor and ECM, particularly at flex points near the engine mount
• Shorted or open circuit caused by connector corrosion from coolant leaks or moisture infiltration at the sensor plug
• Poor ground connection at the ECM ground points (check chassis ground straps for rust)
• Failed ECM (rare, but possible on machines with electrical system damage history)
• Coolant contamination causing sensor element coating or failure

How to Troubleshoot and Fix Code C-2

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check for visible coolant leaks, damaged wiring, or corroded connector pins. On used excavators, examine the wire harness along the frame rail for chafing points where vibration may have worn through insulation.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 68°F (20°C), the sensor should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness voltage at the ECM connector—you should see approximately 5 volts reference voltage with the key on, engine off.

Step 3: Circuit and Ground Verification Check for short circuits by measuring resistance between the sensor signal wire and ground (should read infinite resistance). Verify all ECM ground connections are clean and tight, as corroded grounds are extremely common on older machines operating in wet conditions.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Kobelco or OEM-equivalent coolant temperature sensor. After replacement, clear codes using diagnostic software like Kobelco STARENT or compatible scan tools, then monitor for code recurrence during a heat cycle.

Disclaimer: This guide provides general troubleshooting steps. Always consult the official Kobelco service manual for your specific serial number. Complex electrical diagnostics should be performed by certified technicians with proper diagnostic equipment.