Kobelco SK135SRLC-2 Fault Code B104: Complete Diagnostic Guide

What is Kobelco SK135SRLC-2 Fault Code B104?

Fault Code B104 on the Kobelco SK135SRLC-2 excavator indicates a malfunction in the Body Controller communication circuit, specifically a loss of communication between the ECM (Engine Control Module) and the Body Control Unit via the CAN bus network.

This code appears when the body controller fails to receive or transmit data packets within the specified time frame, typically 2-5 seconds. The CAN (Controller Area Network) bus is the critical communication backbone connecting all electronic modules on this Kobelco model. When this circuit fails, the machine cannot properly coordinate functions between the engine management system and auxiliary body controls like lighting, gauges, and safety interlocks. For the SK135SRLC-2's integrated monitoring system, this communication failure can trigger protective derate modes or prevent certain hydraulic functions from operating correctly.

Common Symptoms

When Code B104 is active on your SK135SRLC-2, operators typically experience:

• Dashboard warning lights flickering or displaying intermittent malfunction indicators, particularly the engine and system alert lamps
• Gauge cluster failures including inoperative fuel level, temperature, or hour meter displays
• Engine derate or limited power mode where hydraulic response becomes sluggish despite no mechanical issues
• Intermittent starting problems or failure of safety interlocks to disengage properly
• Diagnostic display errors showing multiple simultaneous fault codes that appear/disappear randomly

Potential Causes

The most common technical causes for B104 on used SK135SRLC-2 excavators include:

• CAN bus wiring harness damage near the battery box and body controller mount—a known rub point on this model where harnesses contact frame edges during boom articulation
• Corroded or moisture-infiltrated connectors at the body controller module, typically located behind the cab near the right-hand side panel
• Failing body control unit itself, often due to vibration damage or capacitor aging in machines with 5,000+ operating hours
• Voltage irregularities from aging batteries or failing alternators creating communication dropout
• ECM software version incompatibility after aftermarket reprogramming or module replacement

How to Troubleshoot and Fix Code B104

Step 1: Perform Visual Harness Inspection Begin by physically tracing the CAN bus harness (typically twisted orange/green pair) from the ECM to the body controller. On used SK135SRLC-2s, carefully inspect behind the hydraulic tank and along the right frame rail where harnesses flex during operation. Look for abraded insulation, crushed wires, or evidence of previous repairs with electrical tape.

Step 2: Test Connector Integrity and Resistance Disconnect the body controller connector (usually a gray 24-pin Deutsch connector). Using a digital multimeter, measure CAN High to CAN Low resistance—you should read approximately 60 ohms with all modules connected. Check each pin for corrosion or bent terminals. Apply dielectric grease to all connections before reassembly.

Step 3: Verify Power Supply and Ground Circuits With a multimeter, confirm the body controller receives proper battery voltage (12-14V) at power pins and has solid ground continuity (less than 0.5 ohms). Poor grounds are extremely common on used machines due to corrosion at chassis mounting points.

Step 4: Scan with Diagnostic Software Use Kobelco-specific diagnostic software (KAS or equivalent) to monitor real-time CAN bus communication. Check for message dropout rates and verify both ECM and body controller are transmitting. If only one module shows activity, the silent module requires replacement or reprogramming.

For used excavators, always address harness wear and connector corrosion before replacing expensive modules—over 60% of B104 codes resolve with cleaning and proper wiring repairs.

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Disclaimer: This guide provides general diagnostic procedures. Always consult the official Kobelco service manual for your specific serial number and consider professional diagnosis for complex electrical issues. Working with live electrical systems requires proper training and safety precautions.