Kobelco SK135SRLC-2 Fault Code G043: Complete Diagnostic Guide

What is Kobelco SK135SRLC-2 Fault Code G043?

Fault Code G043 indicates a malfunction in the swing motor control system, specifically detecting an abnormal signal or voltage irregularity in the swing motor rotation sensor circuit. This code is part of Kobelco's proprietary diagnostic system that monitors the excavator's hydraulic swing function through the Electronic Control Unit (ECU).

The swing motor rotation sensor provides critical feedback to the ECU about swing speed, direction, and positioning. When this circuit experiences voltage deviations outside the manufacturer's specified range (typically 0.5-4.5V), the system triggers G043 to prevent potential damage to the swing motor assembly. For the SK135SRLC-2 model, this is particularly important because the swing system operates under high hydraulic pressures, and sensor miscommunication can lead to erratic swing behavior or complete system shutdown.

Common Symptoms

Operators experiencing Code G043 may notice:

• Intermittent or complete loss of swing function with the upper structure freezing or responding sluggishly
• Warning light activation on the instrument cluster, often accompanied by a beep alert
• Erratic swing speeds that don't correspond to joystick input intensity
• Swing motor engaging and disengaging unpredictably during operation
• ECU entering derate mode, limiting swing torque to protect hydraulic components

Potential Causes

The most common technical failures triggering G043 in used SK135SRLC-2 excavators include:

• Swing motor rotation sensor failure due to internal wear or contamination from hydraulic fluid seepage
• Damaged wiring harness near the swing motor mounting area where cables experience constant flexing and abrasion
• Corroded or loose connector pins at the sensor plug (especially common in machines operating in wet or coastal environments)
• ECU voltage supply issues from failing alternator output or battery degradation
• Damaged swing motor resolver or encoder caused by physical impact or bearing failure migration
• Grounding problems from rust accumulation on chassis grounding points

How to Troubleshoot and Fix Code G043

Step 1: Visual Inspection Begin by examining the swing motor rotation sensor located on the swing motor housing. Check for physical damage, oil contamination, or loose mounting bolts. Inspect the wiring harness from sensor to ECU for wear points, particularly where cables pass through the center joint and along the swing bearing area—common rub points on used machines.

Step 2: Electrical Testing Using a digital multimeter, perform voltage checks with the ignition on (engine off). The sensor should output 0.5-4.5V DC depending on position. Check connector resistance (should be <1 ohm for continuity) and inspect for corrosion on terminals. Test the power supply circuit ensuring the sensor receives consistent 5V reference voltage from the ECU.

Step 3: Dynamic Testing With Kobelco diagnostic software (or compatible scan tool), monitor live sensor data while manually rotating the swing motor. The voltage signal should change smoothly and proportionally. Erratic readings indicate sensor replacement; stable readings suggest wiring or ECU issues. Clear codes and perform a swing function test.

Step 4: Component Replacement For used excavators, always replace connector seals and apply dielectric grease during sensor replacement to prevent future corrosion. Verify proper harness routing away from heat sources and moving parts.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual and consider professional diagnostic assistance for complex electrical issues, especially when working with high-voltage systems.