What is Kobelco SK200-6E Fault Code B-9?

Kobelco SK200-6E Fault Code B-9 indicates a malfunction in the engine preheating system, specifically related to the glow plug relay circuit or glow plug system failure. This code is triggered when the Engine Control Module (ECM) detects abnormal voltage, current draw, or circuit continuity issues within the preheating system that prepares the diesel engine for cold starts.

This fault is particularly critical for the Kobelco SK200-6E's 6D34-T Mitsubishi engine, as proper glow plug operation is essential for cold-weather starting and complete combustion during warm-up phases. When this system fails, operators may experience extended cranking times, rough idle during cold starts, and increased white smoke emissions, which can accelerate engine wear on used machines already experiencing normal aging.

Common Symptoms

When Code B-9 is active, operators typically experience:

• Hard starting or extended cranking, especially in temperatures below 50°F (10°C)
• Glow plug indicator light staying illuminated longer than normal or flashing intermittently
• Excessive white or gray smoke during initial startup that persists longer than usual
• Rough engine operation for the first several minutes after cold start
• Check engine light illuminated on the instrument cluster, potentially accompanied by reduced engine performance

Potential Causes

The most common technical causes for Code B-9 on used SK200-6E excavators include:

• Failed glow plug relay – The electromagnetic relay controlling power to the glow plugs often fails due to repetitive cycling and heat exposure over years of operation
• Burned-out individual glow plugs – Carbon buildup and thermal stress cause individual plugs to fail (common in machines with 8,000+ hours)
• Corroded or damaged wiring harness – The preheater circuit wiring near the engine block experiences vibration and heat, causing insulation breakdown and shorts to ground
• Poor electrical connections at glow plug terminals or relay connector pins due to corrosion from moisture intrusion
• ECM internal fault – Less common, but the control module's glow plug driver circuit can fail in high-hour machines
• Blown fuse protecting the glow plug circuit in the main fuse box

How to Troubleshoot and Fix Code B-9

Step 1: Visual Inspection and Preliminary Checks

Begin by inspecting the glow plug relay located in the engine compartment fuse/relay box. Listen for an audible "click" when the ignition is turned to the ON position before cranking. Use a digital multimeter to verify battery voltage (approximately 24V on this model) is reaching the relay input terminal. Check the main glow plug fuse for continuity. On used excavators, carefully inspect all wiring harness sections running along the valve cover for chafing, melted insulation, or oil contamination that degrades wire integrity.

Step 2: Test Glow Plug Resistance

Disconnect the power supply bus bar connecting all glow plugs. Using a multimeter set to ohms, test each individual glow plug's resistance from the terminal to engine ground. Specifications typically call for 0.5 to 2.0 ohms per plug (consult service manual for exact values). Any glow plug reading infinite resistance (open circuit) or near-zero resistance (shorted) must be replaced. In used machines with 6,000+ operating hours, replacing all glow plugs as a set prevents repeat failures.

Step 3: Relay and Circuit Testing

Test the glow plug relay by applying battery voltage directly to the control terminals while measuring continuity across the power terminals. A functional relay will show near-zero resistance when energized. Measure voltage drop across the relay during operation—excessive drop (over 0.5V) indicates internal contact degradation. Check for voltage at the glow plug bus bar during the preheat cycle; it should read full battery voltage for 15-30 seconds depending on temperature.

Step 4: Advanced Diagnostics

If all components test normally, connect Kobelco-compatible diagnostic software (or Mitsubishi MUT-III) to read live ECM data during the preheat cycle. Monitor glow plug current draw and compare to specifications (typically 60-80 amps total for six plugs). Check for stored ECM faults that might indicate controller-side issues. Inspect all connector pins at the ECM harness for corrosion or bent terminals—common failure points on used excavators stored outdoors.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual for your specific serial number and year. If you lack experience with high-amperage electrical systems or diesel engine diagnostics, consult a certified heavy equipment technician to prevent equipment damage or personal injury.