Kobelco SK135SR-2 Fault Code B102: Complete Diagnostic Guide

What is Kobelco SK135SR-2 Fault Code B102?

Fault Code B102 on the Kobelco SK135SR-2 excavator indicates a malfunction in the engine pre-heating system circuit, specifically related to the glow plug relay or its control circuit. This code is triggered when the Engine Control Module (ECM) detects an abnormal voltage or current flow in the pre-heating circuit during the ignition-on sequence.

The pre-heating system is critical for cold-start performance on this diesel excavator. When B102 appears, the ECM has identified that the glow plug relay is not responding correctly to commands, potentially due to electrical resistance, open circuits, or relay failure. For used SK135SR-2 machines operating in colder climates, this fault can severely impact starting reliability and increase wear on the starter motor and engine components.

Common Symptoms

When Code B102 is active, operators typically experience:

• Difficult cold starts or extended cranking times, especially in temperatures below 50°F (10°C)
• Glow plug indicator light flashing or remaining illuminated on the instrument panel
• No audible click from the glow plug relay during the pre-heat cycle (normally heard 2-3 seconds after key-on)
• White or gray exhaust smoke during initial startup due to incomplete combustion
• ECM warning light illuminated with stored diagnostic trouble code

Potential Causes

The most common technical causes for B102 on used SK135SR-2 excavators include:

• Failed glow plug relay (relay contacts burned or coil resistance out of specification)
• Damaged wiring harness between the ECM and relay, particularly at the harness routing point near the battery box where vibration causes wire chafing
• Corroded or loose connector pins at the relay socket or ECM connector C-117
• Blown fuse in the glow plug circuit (typically 30A or 40A rated)
• Failed individual glow plugs creating excessive current draw that triggers relay protection
• ECM internal driver circuit fault (less common but possible in high-hour machines)

How to Troubleshoot and Fix Code B102

Step 1: Visual Inspection Locate the glow plug relay in the electrical junction box near the battery compartment. Inspect all connectors for corrosion, bent pins, or moisture intrusion—common issues in used excavators. Check the relay mounting and ground connections for tightness.

Step 2: Test the Glow Plug Relay Remove the relay and test using a multimeter. Measure coil resistance (should be 70-90 ohms typically). Apply 12V directly to the coil terminals and verify the relay clicks and shows continuity across the load terminals. Replace if resistance is out of range or no click occurs.

Step 3: Check Circuit Voltage and Continuity With ignition ON (engine off), use a multimeter to verify battery voltage (12V+) at the relay power supply terminal. Check for ECM command signal (should pulse to ground during pre-heat cycle). Inspect harness continuity between ECM pin C-117-23 and the relay control wire—common failure point due to harness flex near the cab frame.

Step 4: Inspect Individual Glow Plugs If relay tests good, measure resistance of each glow plug (typically 0.5-2.0 ohms). A shorted glow plug will draw excessive current. On used machines, carbon buildup or swollen glow plug tips can cause electrical faults.

Step 5: Clear Code and Verify Repair After repairs, clear the code using Kobelco diagnostic software or a compatible J1939 scan tool. Perform a cold-start test cycle to confirm proper pre-heat operation and verify B102 does not return.

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Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the official Kobelco service manual for your specific serial number range and software version. If unfamiliar with electrical diagnostics, seek assistance from a certified Kobelco dealer or qualified heavy equipment electrician to avoid ECM damage or safety hazards.