Komatsu PC750LC-7 Fault Code AA10NX: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code AA10NX?

Fault Code AA10NX indicates a communication error or abnormal signal detected in the machine's network system, specifically related to the CAN (Controller Area Network) bus communication between the engine controller and other electronic control modules.

This code typically appears when the ECM (Engine Control Module) cannot properly communicate with peripheral controllers such as the hydraulic control unit, monitor panel, or transmission controller. In the PC750LC-7, this network communication is critical for coordinating engine performance with hydraulic demand, ensuring optimal fuel efficiency and preventing component damage. When this communication fails, the machine's integrated systems cannot function harmoniously, potentially leading to reduced performance or complete shutdown.

Common Symptoms

When fault code AA10NX is active, operators typically experience:

• Warning lights illuminated on the monitor panel, often accompanied by error messages indicating communication failure
• Intermittent or complete loss of monitor display functions, including gauge readings and system status indicators
• Reduced engine power or derate mode activation as a protective measure
• Erratic hydraulic response or inconsistent implement control due to disrupted signal coordination
• Engine shutdown in severe cases where the ECM enters failsafe mode

Potential Causes

The most common technical causes for AA10NX in used PC750LC-7 excavators include:

• Damaged or corroded CAN bus wiring harness, particularly at known rub points near the engine mounting area and along the boom base
• Loose or corroded connector pins at the ECM, monitor panel, or junction boxes (especially the main harness connector behind the cab)
• Failed termination resistors within the CAN network causing signal reflection and data corruption
• ECM or controller module failure, though less common than wiring issues in used machines
• Low battery voltage or poor grounding affecting network stability and signal integrity
• Water intrusion into harness connectors from damaged seals or cab leaks

How to Troubleshoot and Fix Code AA10NX

Step 1: Visual Inspection Begin with a thorough inspection of all wiring harnesses along the CAN bus network. Focus on areas where harnesses pass through bulkheads, near moving components, and around the engine bay where heat and vibration are highest. Check all connector pins for corrosion, bent terminals, or moisture intrusion—common issues in used excavators.

Step 2: Voltage and Resistance Testing Using a digital multimeter, verify battery voltage (should be 24-28V on this model) and check all ground connections for resistance below 0.5 ohms. Test CAN bus termination resistance between CAN-H and CAN-L wires at the network endpoints; you should read approximately 60 ohms with all modules connected.

Step 3: Diagnostic Software Analysis Connect Komatsu KOMTRAX or compatible diagnostic software to read detailed network status and pinpoint which specific controller is dropping communication. Monitor live data while wiggling harnesses to identify intermittent connection failures—a critical step for used equipment where wire fatigue is common.

Step 4: Component Replacement If testing reveals a faulty harness section, replace the entire segment rather than splicing, as CAN bus networks require specific twisted-pair wiring. Clean all connector contacts with electrical contact cleaner and apply dielectric grease before reassembly to prevent future corrosion.

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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 services for complex electrical issues, especially when dealing with used equipment where multiple underlying problems may exist.