Komatsu PC300-8M0 Fault Code 879CKB: Complete Diagnostic Guide

What is Komatsu PC300-8M0 Fault Code 879CKB?

Fault Code 879CKB indicates a communication error or data transmission failure within the Komatsu PC300-8M0's CAN (Controller Area Network) bus system, specifically affecting the machine monitoring system or auxiliary controller network.

This diagnostic trouble code (DTC) signals that the Engine Control Module (ECM) or Machine Controller has detected an interruption, abnormal signal, or complete loss of communication between critical electronic control units. The CAN bus serves as the central nervous system for modern excavators, enabling real-time data exchange between the engine management system, hydraulic controllers, and monitoring displays. When this communication breaks down, the machine cannot properly coordinate its systems, potentially leading to performance degradation or safety concerns.

For the PC300-8M0 specifically, this code is critical because this model relies heavily on integrated electronic controls for fuel efficiency optimization and hydraulic system coordination.

Common Symptoms

• Warning lights illuminated on the monitor panel, particularly the malfunction indicator or system error lamp
• Intermittent or complete loss of monitor display functions, including gauge readings and operational data
• Reduced engine power or activation of derate mode as a protective measure
• Erratic hydraulic response or inconsistent implement control due to communication delays
• Inability to access machine diagnostics through the standard display interface

Potential Causes

The most frequent causes of Code 879CKB in used PC300-8M0 excavators include:

• Damaged or corroded CAN bus wiring harness, particularly at known rub points near the engine mounting brackets and along the boom base
• Faulty termination resistors at either end of the CAN network (typically 120-ohm resistors)
• Corroded or loose connector pins at the ECM, machine controller, or junction boxes—common in machines with high operating hours
• Failed auxiliary controller module or monitoring system ECU
• Water intrusion into sealed connectors, especially in machines operated in wet conditions
• Voltage irregularities from aging batteries or failing alternators affecting network stability

How to Troubleshoot and Fix Code 879CKB

Step 1: Visual Inspection Begin with a thorough physical examination of all CAN bus harness routing. Focus on areas where the harness contacts metal surfaces, particularly near the turntable and engine compartment. Check all connector seals for cracks, corrosion (green/white deposits), or moisture. On used excavators, pay special attention to harness sections that show wear from vibration or rubbing.

Step 2: Electrical Testing Using a digital multimeter, measure CAN bus resistance between the CAN-High and CAN-Low terminals with all controllers disconnected. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). Deviation indicates faulty termination resistors or wiring issues. Check for continuity along the entire harness length and verify no shorts to ground exist.

Step 3: Voltage and Signal Verification With the ignition on and controllers connected, measure CAN-High voltage (should read approximately 2.5-3.5V) and CAN-Low voltage (approximately 1.5-2.5V) at multiple points. Use Komatsu KOMTRAX diagnostic software or compatible scan tools to monitor live CAN bus traffic and identify which controller is failing to communicate.

Step 4: Component Replacement If testing reveals a specific failed component, replace the faulty controller, damaged harness section, or corroded connectors. For used machines, consider replacing all termination resistors preventatively, as they degrade over time. Always apply dielectric grease to reconnected terminals to prevent future corrosion.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional assistance for complex electrical diagnostics. Improper repairs to CAN bus systems can cause additional controller damage.