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

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

Fault Code 879DKZ 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 peripheral control modules.

This diagnostic trouble code (DTC) signals that the main controller (ECM) is unable to properly communicate with one or more secondary control units, such as the hydraulic control module, monitor panel, or pump control system. For the PC300-8M0, this is critical because the integrated KOMTRAX system and hydraulic management rely on continuous data exchange between controllers. When communication breaks down, the machine cannot optimize performance or may enter protective derate mode to prevent damage.

Common Symptoms

When fault code 879DKZ is active, operators typically experience:

• Intermittent or complete loss of monitor display functions, including gauge readings and warning indicators
• Reduced hydraulic performance or inconsistent boom/arm response due to controller miscommunication
• Amber or red warning lights illuminated on the instrument cluster
• Engine derate or limited RPM in severe cases where the ECM enters failsafe mode
• KOMTRAX system reporting communication faults or missing data logs

Potential Causes

The most common technical causes for code 879DKZ on used PC300-8M0 excavators include:

• Corroded or damaged CAN bus connectors, particularly at the main harness junction behind the cab (known wear point)
• Frayed or pinched wiring in the harness routing near the swing bearing or along the boom base
• Failed termination resistors on the CAN network (typically 120-ohm resistors at network endpoints)
• Faulty monitor panel or secondary controller with internal communication circuit failure
• Low voltage conditions from aging batteries or poor ground connections affecting signal integrity
• Water intrusion into connector housings, common in machines with compromised cab seals

How to Troubleshoot and Fix Code 879DKZ

Step 1: Visual Inspection Begin by thoroughly inspecting all wiring harnesses along the CAN bus network. Focus on areas where harnesses pass through the swing bearing, near hydraulic lines, and behind the operator cab. Look for chafing, corrosion, or damaged connectors. On used excavators, check for previous repair attempts or aftermarket modifications.

Step 2: Electrical Testing Using a digital multimeter, measure CAN-High and CAN-Low voltage at the main ECM connector. You should see approximately 2.5V on each line at rest, with differential voltage between 1.5-3.5V during communication. Check termination resistance between CAN-High and CAN-Low; it should read approximately 60 ohms with both terminators intact.

Step 3: Diagnostic Software Analysis Connect Komatsu KDPF diagnostic software to identify which specific controller is dropping communication. Monitor live data to see if communication loss is intermittent or permanent. Clear codes and perform a wiggle test on suspect harnesses while monitoring for code recurrence.

Step 4: Component Replacement If testing reveals a specific failed module or corroded connector, replace the affected component. For used machines, always replace connector seals and apply dielectric grease to prevent future corrosion. Verify all ground connections are clean and tight.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic services for complex electrical issues.