What is Komatsu PC110-8M0 Fault Code 879CKA?

Fault Code 879CKA on the Komatsu PC110-8M0 excavator indicates a communication error between the Engine Control Module (ECM) and the Machine Control Module (MCM) or a CAN bus system malfunction. This code signals that critical data exchange between the machine's central control systems has been interrupted or degraded, affecting coordinated operations between the engine and hydraulic systems.

This fault is particularly significant for the PC110-8M0 because this mid-size excavator relies on integrated electronic controls to optimize fuel efficiency, hydraulic response, and emissions compliance. When communication breaks down between the ECM and MCM, the machine cannot properly coordinate engine speed with hydraulic demand, potentially triggering protective derate modes that limit performance.

Common Symptoms

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

• Engine derate mode activated, limiting maximum RPM to approximately 1,200-1,500 RPM regardless of throttle position
• Multiple warning lights illuminated simultaneously on the instrument cluster, including engine and system warnings
• Erratic hydraulic response or sluggish cycle times due to improper engine-hydraulic coordination
• Intermittent loss of dashboard displays or gauge malfunctions, particularly fuel level and hour meter readings
• Difficulty starting or extended cranking time as modules fail to initialize properly

Potential Causes

The most common technical causes for code 879CKA on used PC110-8M0 excavators include:

• CAN bus harness damage at known wear points near the battery box and main wiring junction behind the operator's seat
• Corroded or loose connector pins on the 38-pin ECM connector or 24-pin MCM connector, especially on machines exposed to water or high-humidity environments
• Failed termination resistor on the CAN bus network (120-ohm resistor deterioration)
• ECM or MCM internal failure, though less common than wiring issues in used machines
• Voltage supply problems to either control module, often caused by corroded ground connections at chassis mounting points
• Previous electrical work creating inadvertent shorts or incorrect harness routing causing chafing

How to Troubleshoot and Fix Code 879CKA

Step 1: Visual Harness Inspection Begin with a thorough physical inspection of the CAN bus wiring harness from the ECM (located behind the left-side access panel) to the MCM (beneath the operator's cab). On used PC110-8M0 excavators, check for harness abrasion where cables pass through the bulkhead near the hydraulic tank and around the battery tray—these are known rub points for this model.

Step 2: Connector and Voltage Verification Disconnect and inspect both the ECM connector (38-pin) and MCM connector (24-pin) for corrosion, bent pins, or moisture intrusion. Clean connectors with electrical contact cleaner and check for proper seating. Using a digital multimeter, verify supply voltage at pin 1 (should read 24V) and check ground continuity at pin 38 on the ECM connector (should read less than 0.5 ohms resistance to chassis ground).

Step 3: CAN Bus Continuity and Resistance Testing With connectors disconnected and ignition off, measure resistance between CAN-High and CAN-Low terminals. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). If you read 120 ohms, one termination resistor has failed. If open circuit (infinite resistance), there's a break in the CAN bus wiring. Use Komatsu's KOMTRAX diagnostic software or an aftermarket tool compatible with J1939 protocol to monitor live CAN bus traffic and identify communication drop-outs.

Step 4: Component Replacement Priority For used excavators, replace suspect components in this order: first, damaged harness sections or corroded connectors; second, failed termination resistors; third, the MCM (less expensive); finally, the ECM. Always clear codes and test operation between replacements to avoid unnecessary parts replacement.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues. Improper electrical work may cause additional damage to sensitive electronic components.