What is Kobelco SK350LC-8 Fault Code D063?

Fault Code D063 on the Kobelco SK350LC-8 excavator indicates a malfunction in the Machine Control Unit (MCU) communication system, specifically a communication error between the engine ECM (Engine Control Module) and the machine's main controller. This diagnostic trouble code typically signals that data transmission between these critical control systems has been interrupted or degraded beyond acceptable parameters.

The SK350LC-8 relies on continuous CAN bus (Controller Area Network) communication between the ECM and MCU to coordinate engine performance with hydraulic demand, implement power modes, and manage fuel efficiency. When communication fails, the machine's integrated control system cannot properly optimize performance. This is particularly critical on the SK350LC-8 because the ITSL (Integrated Traction System Logic) depends on real-time data exchange to balance engine output with hydraulic load requirements. Without proper communication, the excavator may enter a protective derate mode to prevent damage.

Common Symptoms

• Warning light illumination on the instrument cluster, typically the engine or system malfunction indicator
• Reduced engine power or automatic derate to lower RPM, limiting hydraulic performance and cycle times
• Intermittent loss of power modes – inability to switch between economy and power work modes
• Delayed throttle response when operating hydraulic functions under load
• Display screen errors showing communication fault messages or blank sections on the multi-information display

Potential Causes

The most common technical causes for D063 on used SK350LC-8 excavators include:

• Corroded or loose CAN bus connectors at the ECM or MCU – particularly the 38-pin connector behind the cab on the right-hand side, which is exposed to moisture and vibration
• Damaged wiring harness along known rub points, especially where the main harness passes through the swing bearing and near the battery box mounting bracket
• Failed termination resistors on the CAN bus network (120-ohm resistors that prevent signal reflection)
• ECM or MCU internal failure due to voltage spikes or age-related component degradation common in machines over 8,000 operating hours
• Weak battery voltage or poor ground connections causing intermittent communication dropout during high electrical load conditions
• Aftermarket accessory interference from improperly installed devices tapping into the CAN network

How to Troubleshoot and Fix Code D063

Step 1: Visual Inspection and Connector Check Begin by inspecting all CAN bus connectors between the ECM (located on the left side of the engine) and the MCU (mounted under the operator's seat). Look specifically for green corrosion, bent pins, or moisture intrusion. On used excavators, pay special attention to the main harness connector near the swing bearing – this is a notorious failure point on the SK350LC-8. Clean all connections with electrical contact cleaner and apply dielectric grease before reconnecting.

Step 2: CAN Bus Continuity and Resistance Testing Using a digital multimeter, measure resistance across the CAN-High and CAN-Low wires at the ECM connector with all power off. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). If you read infinite resistance, there's an open circuit in the network. If below 40 ohms, suspect a short circuit or failed termination resistor. Check for 120-ohm resistance at each termination point individually to verify resistor integrity.

Step 3: Voltage and Signal Verification With the ignition on (engine off), measure voltage at the ECM CAN-High and CAN-Low terminals. You should see approximately 2.5V DC on each line when idle. During communication (key on, waiting for initial system check), use an oscilloscope or Kobelco diagnostic software (CAPS) to verify signal transmission. CAPS software will show real-time communication status and help isolate whether the ECM or MCU is failing to transmit.

Step 4: Harness Routing Inspection for Used Equipment For used SK350LC-8 excavators, physically trace the main harness from ECM to MCU, checking for abrasion damage at: the swing bearing transition point, the battery tray mounting area, and where the harness contacts the chassis near the hydraulic tank. Look for wear marks, exposed copper, or previous repair attempts using inappropriate wire or connectors. Replace any damaged sections with OEM-spec harness assemblies, not field splices, as signal integrity is critical.

Step 5: Ground Circuit Verification Test ground integrity at both the ECM and MCU mounting points. Resistance to chassis ground should be less than 0.5 ohms. On older machines, corrosion at ground points causes erratic communication errors. Remove ground connections, sand contact surfaces to bare metal, and reinstall with star washers.

Disclaimer: While this guide provides comprehensive troubleshooting steps, CAN bus diagnostics can be complex. If you're uncomfortable with electrical testing or lack proper diagnostic tools, consult a certified Kobelco technician or qualified heavy equipment electrician. Incorrect repairs to communication networks can cause additional fault codes or damage control modules.