What is Kobelco SK130-8 Fault Code 6591?

Fault Code 6591 on the Kobelco SK130-8 excavator indicates a communication error or malfunction within the machine's Controller Area Network (CAN) system, specifically related to data transmission between the engine ECM (Engine Control Module) and the machine's main controller. This diagnostic trouble code (DTC) signals that critical operational data is not being properly shared between control systems, potentially affecting the excavator's performance monitoring and safety functions.

The CAN bus system serves as the digital nervous system of modern excavators, allowing the ECM, hydraulic controllers, and display systems to communicate in real-time. When Code 6591 triggers, it means the Kobelco diagnostic system has detected incomplete, corrupted, or absent data packets traveling between controllers. This is particularly critical on the SK130-8 because this model relies heavily on integrated electronic controls for fuel management, hydraulic optimization, and emission compliance. Interrupted CAN communication can prevent proper engine load calculations and may force the machine into a protective derate mode.

Common Symptoms

When Fault Code 6591 is active on your Kobelco SK130-8, operators typically experience:

• Dashboard warning lights illuminating, particularly the engine malfunction indicator or communication error symbol
• Intermittent loss of display information on the monitor panel, including engine temperature, hydraulic pressure readings, or hour meter
• Erratic gauge behavior where instrument readings fluctuate or freeze unexpectedly
• Reduced engine power or activation of derate mode limiting maximum RPM to protect the engine
• Inability to access diagnostic menus or error history through the standard operator interface

Potential Causes

The most common technical causes for Code 6591 on used SK130-8 excavators include:

• Corroded or damaged CAN bus connectors – especially at the ECM harness connection point near the battery box where moisture accumulation is common
• Broken or frayed CAN bus wiring caused by harness rubbing against frame components or hydraulic lines during thousands of operating hours
• Failed termination resistors within the CAN network (standard 120-ohm resistors that maintain signal integrity)
• ECM internal communication module failure due to voltage spikes or age-related component degradation
• Loose ground connections at the main controller or ECM mounting points, creating voltage reference issues
• Aftermarket accessory interference from improperly installed telematics devices or non-OEM monitoring systems tapped into the CAN network

How to Troubleshoot and Fix Code 6591

Step 1: Visual Inspection of Wiring and Connectors

Begin with a thorough physical examination of the CAN bus harness, which typically consists of a twisted pair of wires (often orange/green or yellow/green on Kobelco equipment). On used excavators, focus on areas where the harness passes through the swing bearing assembly and near the engine bay where heat and vibration are highest. Disconnect the main ECM connector (typically an 80-pin or dual 40-pin connector) and inspect for:

• Green corrosion on pins (indicates moisture intrusion)
• Bent or pushed-back pins that may have lost contact
• Cracks in the connector housing

Use electrical contact cleaner and a soft brush to clean all pins, then apply dielectric grease before reconnecting.

Step 2: Test CAN Bus Continuity and Resistance

Using a digital multimeter (DMM), measure the resistance between the CAN-High and CAN-Low wires at the ECM connector with all power disconnected and the key removed. You should read approximately 60 ohms (two 120-ohm terminating resistors in parallel across the network).

• Reading of 120 ohms indicates one terminating resistor has failed or a break exists in the network
• Infinite resistance (OL) suggests a complete circuit break
• 0-5 ohms indicates a short circuit between CAN wires

Check continuity of each CAN wire individually from the ECM to the main controller (typically located under the operator cab). On used machines, pay special attention to wire routing near moving components and check for insulation wear.

Step 3: Verify Power Supply and Grounds

Code 6591 can be triggered by voltage irregularities affecting the CAN transceivers. With the key on but engine off, verify:

• Battery voltage at the ECM power supply pin reads 12-14V DC
• All ECM and controller ground connections show less than 0.1 ohms resistance to chassis ground
• The ignition-switched power supply to the main controller is stable (not dropping when accessories are activated)

On older SK130-8 machines, ground connections frequently corrode where the grounding straps attach to painted surfaces. Remove, clean to bare metal with a wire brush, and reinstall with star washers.

Step 4: Advanced Diagnostics with Kobelco Software

Connect Kobelco diagnostic software (SIMS - Service Information Management System) or a compatible CAN bus analyzer to monitor live data traffic. This allows you to:

• Identify which specific controller is failing to transmit
• Observe error frame rates on the network
• Monitor message identifiers to pinpoint communication breakdowns

If specialized software isn't available, some generic heavy equipment diagnostic scanners with CAN bus monitoring capabilities can identify whether the ECM or main controller is the non-communicating component.

Step 5: Component Replacement Based on Findings

After isolating the fault location:

• Replace damaged harness sections with OEM Kobelco wiring (using proper twisted-pair CAN cable, not standard automotive wire)
• Install new termination resistors if testing revealed incorrect resistance values
• Replace the ECM or main controller only after confirming all wiring, grounds, and power supplies are correct—on used excavators, wiring issues are far more common than actual controller failures

Critical Note for Used Excavators: Before replacing expensive electronic components, always verify that previous repairs haven't introduced problems. Check for non-standard splices, aftermarket accessories connected to the CAN bus, or repaired connectors that may have created intermittent connections. Corrosion and mechanical wear cause the majority of CAN communication failures in machines with over 5,000 operating hours.

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Disclaimer: This guide provides general troubleshooting information for Kobelco SK130-8 excavators experiencing Fault Code 6591. Electrical diagnostics involve working with complex control systems and should be performed by qualified heavy equipment technicians. Always consult the official Kobelco service manual for your specific machine serial number, and use proper safety procedures when working with electrical systems. Improper diagnosis can lead to additional damage or safety hazards.