What is Kobelco SK140LC-8 Fault Code 06638?

Fault Code 06638 on the Kobelco SK140LC-8 excavator indicates a communication error between the Engine Control Module (ECM) and the Controller Area Network (CAN) bus system. This code specifically signals that the ECM is detecting irregular or interrupted data transmission across the machine's networked control systems.

The CAN bus serves as the digital nervous system for modern excavators, allowing the ECM, hydraulic controllers, instrument cluster, and other electronic modules to share critical operational data. When code 06638 triggers, the ECM cannot properly communicate with one or more controllers, potentially affecting engine performance coordination, hydraulic function integration, and diagnostic capabilities. For the SK140LC-8's Hino J05E engine and integrated hydraulic system, this communication breakdown can lead to performance limitations as the machine enters protective derate modes to prevent damage from uncoordinated system operation.

Common Symptoms

• Check engine light or malfunction indicator illuminated on the instrument panel
• Power derate mode where the excavator operates at reduced engine RPM and hydraulic flow
• Erratic gauge readings or complete loss of display functions on the monitor panel
• Intermittent functionality where systems work normally then suddenly enter fault mode
• Multiple fault codes appearing simultaneously across different systems due to communication loss

Potential Causes

On used SK140LC-8 excavators, fault code 06638 typically stems from physical deterioration rather than component failure. The most common causes include:

Corroded or damaged CAN bus connectors behind the operator cab where moisture intrusion is prevalent on older machines. The main harness connector near the turntable bearing experiences constant flexing during swing operations, causing wire fatigue and intermittent connections.

Chafed wiring harness along the right-hand boom area where the main CAN wiring runs alongside hydraulic lines—vibration over thousands of operating hours wears through protective sheathing.

Failed termination resistors at CAN bus endpoints, which are critical for maintaining proper signal integrity across the network.

ECM or controller internal faults due to voltage spikes from starting system issues or corroded ground connections.

Weak battery voltage or alternator output problems creating voltage fluctuations that disrupt CAN communication protocols.

How to Troubleshoot and Fix Code 06638

Step 1: Visual Harness Inspection Before connecting diagnostic equipment, perform a thorough physical inspection. Check the main wiring harness from the ECM (located under the operator platform) along its entire route to the front attachment. Look specifically at flex points near the turntable and behind the cab. Inspect all CAN bus connectors for corrosion (green oxidization), pushed-back pins, or moisture contamination. On used machines, pay special attention to areas where harnesses contact metal edges or hydraulic lines.

Step 2: Voltage and Resistance Testing Using a digital multimeter, verify battery voltage is 12.5-14.5V with the engine running. Test CAN-High and CAN-Low wiring resistance—you should measure approximately 60 ohms between CAN-H and CAN-L with all controllers connected. Check the termination resistors (typically 120 ohms each at network endpoints). Measure voltage at the ECM connector with ignition on: CAN-H should read approximately 2.5-3.5V, CAN-L around 1.5-2.5V.

Step 3: Diagnostic Software Analysis Connect Kobelco-specific diagnostic software (or compatible J1939 diagnostic tool) to read detailed communication fault data. Monitor real-time CAN bus activity to identify which controller is dropping from the network. Clear codes and perform a CAN bus snapshot test while operating the machine to capture intermittent faults. Check for stored diagnostic trouble codes in all modules, not just the ECM.

Step 4: Repair and Verification Address identified issues systematically. For corroded connectors, clean with electrical contact cleaner and apply dielectric grease. Replace damaged harness sections with OEM Kobelco wiring maintaining proper shielding and routing. If termination resistors failed, install new 120-ohm resistors at proper network endpoints. After repairs, clear all fault codes, cycle the ignition, and run the machine through operational cycles while monitoring for code recurrence.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Complex CAN bus diagnostics may require factory-level diagnostic tools and training. Always consult Kobelco service documentation and consider professional technical support for persistent communication faults, especially on used equipment where underlying electrical system degradation may exist.