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

Fault Code B-6 on the Kobelco SK200-6E indicates a malfunction in the boom raising solenoid valve circuit. This code is triggered when the machine's Electronic Control Module (ECM) detects an abnormal electrical signal—either an open circuit, short circuit, or resistance value outside the specified range—in the wiring or components controlling the boom raise function.

The SK200-6E uses a proportional solenoid valve system to control hydraulic flow to the boom cylinder. When the solenoid valve or its control circuit fails, the ECM cannot properly regulate boom movements, compromising both productivity and safety. This is especially critical on used excavators where electrical connectors and wiring harnesses may have degraded from years of vibration, moisture exposure, and heat cycling.

Common Symptoms

• Boom control becomes erratic or unresponsive when attempting to raise the boom
• Warning light or error message displayed on the monitor panel specifically referencing hydraulic system fault
• Boom may operate in one direction only (lowering works, but raising is slow or non-functional)
• Intermittent loss of boom function, particularly when the machine is cold or after extended operation
• ECM may limit engine RPM or enter a derated mode to protect the hydraulic system

Potential Causes

The most common causes of Code B-6 on used SK200-6E excavators include:

• Damaged or corroded wiring harness between the ECM and boom raise solenoid valve, particularly at harness routing points near the swing bearing or boom pivot
• Failed boom raise solenoid valve coil due to internal short circuit or open winding (resistance typically should measure 10-15 ohms)
• Corroded or loose connector pins at the solenoid valve plug, often caused by water intrusion through deteriorated seals
• ECM internal driver circuit failure, though less common than external wiring issues
• Chafed wires at known wear points where the harness contacts the cab frame or hydraulic lines during swing or boom operation

How to Troubleshoot and Fix Code B-6

Step 1: Visual Inspection Begin by thoroughly inspecting the wiring harness from the ECM to the boom raise solenoid valve. On used excavators, pay special attention to areas where the harness passes through the swing bearing and along the boom structure. Look for abraded insulation, corroded connectors, or oil-soaked wiring that indicates seal failures.

Step 2: Electrical Testing Using a digital multimeter, disconnect the solenoid valve connector and measure the coil resistance. Kobelco specifications typically call for 10-15 ohms at room temperature. Next, check for continuity in the control wiring back to the ECM—there should be no resistance to ground on either control wire. Measure voltage supply at the connector with the ignition on; you should see battery voltage on the power supply wire.

Step 3: Functional Testing and Component Replacement If resistance and voltage values are correct, use Kobelco diagnostic software to command the solenoid valve while monitoring current draw. Normal operation should show 0.5-1.5 amps. If the solenoid tests faulty, replacement is necessary. However, on older machines, always clean connector terminals with electrical contact cleaner and apply dielectric grease to prevent recurring corrosion before reinstalling or replacing components.

Step 4: Verify Repair After repairs, clear the fault code using diagnostic software, cycle the boom through full range of motion, and monitor for code recurrence. Check all connector strain reliefs and secure any loose harness routing to prevent future chafing.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual for your specific machine serial number and seek assistance from a certified heavy equipment technician for complex electrical diagnostics or hydraulic system repairs.