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

Fault Code 879AKA on the Komatsu PC110-8M0 indicates a communication error or abnormal signal between the Engine Control Module (ECM) and the machine's hydraulic control system. This diagnostic trouble code (DTC) specifically points to an interruption in the CAN bus network or incompatible data transmission affecting the excavator's integrated control systems.

The PC110-8M0 utilizes a sophisticated networked control architecture where the ECM, pump control module, and monitor panel continuously exchange operational data. When code 879AKA triggers, it signals that critical machine parameters—such as engine load, pump demand, or throttle position—are not being properly communicated between modules. This is particularly problematic in this model because the hydraulic pump control relies on real-time engine data to optimize performance and fuel efficiency. Failure in this communication chain can lead to improper load management, reduced machine responsiveness, and potential damage to hydraulic components due to mismatched operating parameters.

Common Symptoms

• Warning light illuminated on the instrument cluster, often accompanied by reduced engine power or hydraulic system derate mode
• Erratic hydraulic response, including inconsistent boom or arm speed, or delayed response to joystick commands
• Engine operating in fixed RPM mode, ignoring throttle dial adjustments or auto-idle functions not working properly
• Monitor panel displaying error messages or showing incorrect engine/hydraulic temperature readings
• Intermittent loss of machine functions that return to normal after key cycle, indicating unstable network communication

Potential Causes

Wiring harness damage is the most common culprit in used PC110-8M0 machines, particularly where the main harness passes near the swing motor or along the boom base where repetitive movement causes insulation wear and wire exposure.

Corroded or loose connector pins at the ECM, pump controller, or junction boxes—especially machines operated in marine, mining, or coastal environments where salt and moisture accelerate corrosion.

Faulty ECM or pump control module due to age-related component failure, though this is less common than harness issues in older machines.

Low battery voltage or poor grounding affecting CAN bus signal integrity—critical in machines with aftermarket electrical accessories or battery systems nearing end-of-life.

Software version mismatch between control modules, particularly if components have been replaced without proper calibration or if ECM updates weren't applied to all networked modules simultaneously.

How to Troubleshoot and Fix Code 879AKA

Step 1: Visual Inspection of Wiring Harnesses Begin by thoroughly inspecting the main engine harness and pump control wiring for visible damage, particularly at flex points near the swing bearing and along the right-hand chassis rail. Look for abraded insulation, pinched wires, or evidence of rodent damage. On used excavators, pay special attention to connector boots—cracked boots allow moisture intrusion leading to terminal corrosion.

Step 2: Check CAN Bus Voltage and Resistance Using a digital multimeter, measure CAN-High and CAN-Low voltage at the ECM connector (typically pins designated in the service manual). With ignition on and engine off, you should read approximately 2.5V on CAN-High and 2.5V on CAN-Low at rest. Measure termination resistance between CAN-High and CAN-Low across the network—proper termination should show approximately 60 ohms. Deviations indicate open circuits, shorts, or missing termination resistors.

Step 3: Inspect ECM and Controller Grounds Verify all ground connections at the ECM, pump controller, and battery are clean, tight, and free of corrosion. Remove ground terminals, wire-brush both the terminal and mounting surface, and reinstall with electrical contact grease. Poor grounds are epidemic in used machines and create voltage reference issues affecting digital communications.

Step 4: Use Komatsu Diagnostic Software Connect Komatsu KOMTRAX or compatible diagnostic software to access detailed fault information and monitor real-time CAN bus traffic. Check for additional stored codes that may indicate which specific module is failing to communicate. Perform active tests to command hydraulic functions while monitoring communication status to identify intermittent failures.

Step 5: Replace Damaged Components If testing isolates a specific harness section, repair using OEM-spec wire and weatherproof connectors rather than replacing entire harnesses when possible—this saves significant costs on used equipment. If a control module is confirmed faulty, ensure replacement units have compatible software versions and perform ECM parameter initialization after installation.

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Disclaimer: This guide provides general troubleshooting information. Fault code diagnosis on heavy equipment should be performed by qualified technicians with proper tools and safety equipment. Always consult the official Komatsu service manual for your specific machine serial number and follow all safety protocols when working on electrical and hydraulic systems.