What is Kobelco SK200-6 Fault Code B-15?

Fault Code B-15 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 generated when the Electronic Control Module (ECM) detects abnormal current flow, resistance values, or circuit continuity issues within the preheating system during cold start sequences.

The glow plug system is critical for diesel engine starting, especially in cold weather conditions. When B-15 triggers, the ECM has identified that the glow plugs are not receiving proper voltage, the relay has failed, or there's an open/short circuit in the preheating harness. For the Kobelco SK200-6's 6D34-T engine, proper preheating ensures complete combustion during startup, reduces white smoke emissions, and prevents excessive wear on engine components during cold starts.

Common Symptoms

• Hard starting or extended cranking time, particularly in cold ambient temperatures below 40°F (4°C)
• Glow plug indicator light remains illuminated longer than normal or fails to activate entirely
• Excessive white smoke from the exhaust during initial startup due to incomplete fuel combustion
• Rough idle for the first 1-3 minutes after cold start until engine reaches operating temperature
• Diagnostic display showing B-15 code on the monitor panel, often accompanied by reduced engine performance warnings

Potential Causes

The most common technical failures triggering B-15 on used SK200-6 excavators include:

• Glow plug relay failure – internal contacts become corroded or burned out after extended service life
• Failed individual glow plugs – carbon buildup or element burnout (common after 3,000-5,000 operating hours)
• Damaged wiring harness at known rub points near the engine block mounting brackets or valve cover
• Corroded connector terminals at the glow plug relay socket or individual glow plug connections
• ECM power supply issues affecting the preheating circuit output voltage
• Blown fuse in the glow plug circuit (typically a 30A fuse in the main power distribution box)

How to Troubleshoot and Fix Code B-15

Step 1: Visual Inspection and Preliminary Checks Begin by inspecting the glow plug relay located in the engine compartment fuse box. Check for corrosion, loose connections, or signs of overheating. On used excavators, examine the wiring harness routing from the relay to each glow plug for chafing, particularly where it contacts the engine block or passes through metal brackets.

Step 2: Electrical Testing with Multimeter Using a digital multimeter, test the glow plug relay operation. With the key in the "ON" position (engine not running), you should measure battery voltage (approximately 24V) at the relay output terminal during the preheat cycle. Test each individual glow plug resistance by disconnecting the power lead and measuring between the glow plug terminal and engine ground – readings should be 0.5-2.0 ohms for functional plugs. Higher resistance or infinite readings indicate failed glow plugs requiring replacement.

Step 3: Circuit Continuity and Load Testing Check the relay coil resistance (should be 70-90 ohms) and verify proper ground connections. For used machinery, perform a voltage drop test across all connector terminals in the circuit while activating the preheat system – drops exceeding 0.5V indicate corroded connections needing cleaning or replacement. If all glow plugs and wiring test satisfactory, use Kobelco diagnostic software (or compatible scan tool) to monitor ECM commanded versus actual glow plug current draw, which should be 15-20 amps per plug.

Step 4: Component Replacement and Verification Replace failed components starting with the most common failures: glow plugs (replace all simultaneously on high-hour machines), relay, or damaged harness sections. After repairs, clear the B-15 code using the diagnostic tool, perform a cold start test, and monitor for code recurrence. On used excavators with over 8,000 hours, consider preventive replacement of the entire glow plug set and relay even if only one component failed.

---

Disclaimer: This guide provides general troubleshooting information for Kobelco SK200-6 excavators. Always consult the manufacturer's service manual for your specific serial number and software version. If you're uncomfortable performing electrical diagnostics, consult a certified Kobelco technician or qualified heavy equipment mechanic to prevent further damage to the electrical system.