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

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

Fault Code B-3 on the Kobelco SK200-6 excavator indicates a malfunction in the engine preheating system, specifically related to the glow plug relay circuit or glow plug operation. This code is triggered when the Engine Control Module (ECM) detects abnormal resistance, voltage irregularities, or circuit continuity failures in the preheating system during cold start sequences.

The preheating system is critical for diesel engine combustion efficiency, particularly in cold weather conditions. When B-3 appears, the glow plugs may not be heating adequately, which compromises fuel atomization and can lead to hard starting, excessive white smoke, and incomplete combustion. For the Kobelco SK200-6's 6D34-T engine, proper glow plug function is essential to achieve optimal cylinder temperatures for reliable ignition.

Common Symptoms

When fault code B-3 is active, operators typically experience:

• Difficult cold starting or extended cranking time, especially in temperatures below 40°F (4°C)
• Excessive white or gray smoke during initial startup that persists longer than normal
• Rough idling for the first 2-3 minutes after cold start until engine reaches operating temperature
• Glow plug indicator light remains illuminated longer than usual or flashes intermittently
• Engine hesitation or misfiring during warm-up phase before reaching normal operating temperature

Potential Causes

The most common technical reasons for B-3 code activation on used SK200-6 machines include:

• Failed glow plug relay due to contact wear or coil burnout (common after 5,000+ hours)
• Individual glow plug failure from carbon buildup or element burnout
• Damaged wiring harness near the engine block where heat cycling causes insulation cracking
• Corroded connector terminals at the glow plug relay or individual plug connections (especially in high-humidity environments)
• Low battery voltage preventing adequate current flow to energize the relay and glow plugs
• Faulty ECM output circuit controlling the relay activation signal
• Blown fuse in the glow plug power supply circuit (check 30A fuse in main power distribution box)

How to Troubleshoot and Fix Code B-3

Step 1: Visual Inspection and Voltage Verification

Begin by checking battery voltage with a digital multimeter—it should read 12.4V minimum with engine off. Inspect the glow plug relay (located on the right side of the engine compartment near the fuel filter) for heat damage, corrosion, or burnt terminals. Check all wiring harnesses running along the valve cover for chafing, especially where they contact the engine block—this is a known wear point on used SK200-6 machines.

Step 2: Relay and Circuit Testing

Using your multimeter, test the glow plug relay coil resistance (should be 70-90 ohms). With the key in the "ON" position during preheat cycle, verify 12V signal from the ECM at the relay control terminal. If voltage is present but relay doesn't click, replace the relay. If no voltage appears, suspect ECM output failure or damaged control wiring.

Step 3: Individual Glow Plug Testing

Disconnect each glow plug connector and measure resistance from the plug terminal to engine ground. Proper resistance should be 0.5-2.0 ohms per plug. Any reading above 5 ohms or infinite resistance indicates a failed glow plug requiring replacement. On used excavators, inspect connector pins for green corrosion (copper oxidation) and clean with electrical contact cleaner and dielectric grease before reassembly.

Step 4: Harness Integrity and Ground Path

Check the main ground strap from engine block to frame for tightness and corrosion. In used machines, vibration often loosens ground connections, creating high-resistance paths that affect glow plug current. Inspect the power supply wire from the battery to the relay for voltage drop—should not exceed 0.5V under load.

Professional Tip for Used Equipment: Before replacing expensive components, thoroughly inspect all connector seals and boots for age-related cracking. On machines with 8,000+ hours, preventive replacement of the entire glow plug harness often resolves intermittent B-3 codes more reliably than individual repairs.

---

Disclaimer: This guide provides general diagnostic procedures for informational purposes. Always consult the official Kobelco service manual for your specific machine serial number. If you lack proper diagnostic tools or experience with high-current electrical systems, contact a certified Kobelco technician to prevent equipment damage or personal injury.