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

Fault Code F-2 on the Kobelco SK250-6E indicates a malfunction in the engine preheating system, specifically related to the glow plug circuit or glow plug relay failure. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects abnormal resistance, voltage irregularities, or a complete circuit failure in the engine's cold-start assist system.

The glow plug system is critical for reliable cold-weather starting on this Isuzu-powered excavator. The ECM monitors current flow to the glow plugs during the preheat cycle. When this Kobelco model encounters F-2, it signals that one or more glow plugs have failed, the glow plug relay is malfunctioning, or there's a wiring harness issue preventing proper preheating. For used SK250-6E machines operating in colder climates, this fault can lead to difficult starting, excessive white smoke during cold starts, and increased engine wear from incomplete combustion during warm-up.

Common Symptoms

• Hard starting or no-start condition in cold weather (below 40°F/4°C)
• Extended cranking time before the engine fires, particularly during morning starts
• Excessive white or gray smoke immediately after cold start, indicating unburned fuel
• Glow plug indicator light staying illuminated longer than normal or flashing during operation
• Rough idle for the first 2-5 minutes after cold start until engine reaches operating temperature

Potential Causes

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

• Failed glow plugs due to carbon buildup or element burnout (typical lifespan: 3,000-5,000 hours)
• Faulty glow plug relay causing intermittent or no power delivery to the glow plug circuit
• Damaged wiring harness between the ECM and glow plugs, especially near the engine block where vibration and heat cause insulation breakdown
• Corroded electrical connectors at glow plug terminals (common in high-humidity environments or machines with coolant leaks)
• ECM internal fault in the glow plug control circuit (rare, but documented on higher-hour machines)
• Poor ground connections at the engine block affecting circuit continuity

How to Troubleshoot and Fix Code F-2

Step 1: Visual Inspection Begin by inspecting the glow plug wiring harness for obvious damage, especially where it runs along the valve cover. On used SK250-6E models, check for harness chafing against the fuel lines or exhaust manifold heat shields. Inspect all electrical connectors for corrosion, oil contamination, or loose terminals.

Step 2: Test Glow Plug Relay Locate the glow plug relay in the main fuse box near the battery compartment. Using a digital multimeter (DMM), check for 12V supply voltage at the relay input terminal with the key in the "ON" position. Listen for an audible click when activating the preheat cycle. Test relay output voltage—should read battery voltage (approximately 24V on this model) when activated.

Step 3: Individual Glow Plug Testing Disconnect the bus bar connecting the glow plugs. Using your multimeter set to resistance mode (ohms), test each glow plug individually. A functioning glow plug should read 0.5-2.0 ohms resistance. Readings above 5 ohms or infinite resistance indicate a failed glow plug. On used machines, replace all glow plugs as a set even if only one tests bad—they typically fail within similar timeframes.

Step 4: Circuit Continuity Check Test wiring continuity between the ECM connector (Pin C-22 for glow plug control) and the relay. Check for voltage drop across connections—should be less than 0.2V. Clean all ground connections at the engine block with a wire brush and apply dielectric grease.

Step 5: Clear Code and Monitor After repairs, clear the fault code using Kobelco's diagnostic software or a compatible J1939 scan tool. Perform a cold start test to verify proper glow plug operation. The preheat indicator should illuminate for 5-15 seconds depending on ambient temperature.

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Disclaimer: This guide provides general troubleshooting information for the Kobelco SK250-6E. Electrical system diagnosis should be performed by qualified technicians with proper training. Always consult the factory service manual and follow lockout/tagout procedures before performing electrical diagnostics. Improper testing can damage the ECM or create safety hazards.