What is Komatsu PC1250-11R Fault Code A900N6?

Fault Code A900N6 indicates a communication error or malfunction in the Network 6 system, specifically related to the CAN (Controller Area Network) bus communication failure between the main controller and peripheral control modules. This code is part of Komatsu's advanced diagnostic system that monitors real-time data transmission between the machine's Electronic Control Module (ECM), hydraulic controllers, and monitoring systems.

The PC1250-11R relies heavily on continuous digital communication between its multiple control units to optimize hydraulic performance, engine management, and operational safety. When Network 6 experiences disruption, the machine cannot properly coordinate functions between systems, potentially leading to reduced performance or complete operational shutdown. This is particularly critical in this 125-ton class excavator where precise hydraulic control depends on millisecond-accurate data exchange between controllers.

Common Symptoms

• Warning light illumination on the monitor panel with "Network Error" or communication fault displayed
• Reduced engine power or hydraulic system operating in limp/derate mode to protect components
• Intermittent loss of monitor display functions, including loss of real-time operating data
• Erratic hydraulic responses or delayed actuator movements due to interrupted command signals
• Multiple secondary fault codes appearing simultaneously as downstream controllers lose communication

Potential Causes

The most common technical causes for A900N6 in used PC1250-11R excavators include:

• CAN bus wiring harness damage from abrasion at known rub points near the swing bearing and boom base where cables flex repeatedly
• Corroded or moisture-contaminated connectors in the main wiring harness, particularly the 38-pin connector behind the operator cab
• Failed termination resistors (120-ohm) at either end of the Network 6 CAN bus line
• ECM internal communication module failure due to voltage spikes or age-related component degradation
• Damaged or pinched shielded cable in the engine compartment where harnesses route near hot exhaust components
• Loose or corroded ground connections affecting the CAN bus signal integrity

How to Troubleshoot and Fix Code A900N6

Step 1: Initial Visual Inspection Begin by thoroughly inspecting all wiring harnesses along the Network 6 circuit path. On used excavators, focus on high-flex areas where the harness passes through the swing bearing area and along the boom cylinder mounts. Look for abraded insulation, crushed cables, or evidence of previous repairs. Check all connector pins for corrosion, bent terminals, or moisture intrusion—especially the large multi-pin connectors near the battery box.

Step 2: Resistance and Continuity Testing Using a digital multimeter, disconnect power and measure CAN High and CAN Low wire resistance. With the network disconnected at both ends, you should measure approximately 60 ohms between CAN-H and CAN-L (two 120-ohm termination resistors in parallel). Test continuity of each wire individually from ECM to peripheral controllers. Resistance should be less than 5 ohms per wire. Check for shorts to ground (should read infinite resistance).

Step 3: Diagnostic Software Analysis Connect Komatsu KOMTRAX or aftermarket diagnostic software to read real-time network status. Monitor communication packet success rates between modules. If specific controllers show zero communication, isolate that branch of the network. Check voltage levels on CAN-H (should read 2.5-3.5V at rest) and CAN-L (1.5-2.5V at rest) with key on, engine off.

Step 4: Component Replacement and Verification For used machines, replace any damaged shielded CAN cable sections with OEM-spec wire (twisted pair with drain wire). Clean all connector contacts with electrical contact cleaner and apply dielectric grease. Verify termination resistors are present and functional at network endpoints. If harness and connections test good, suspect ECM internal failure and consider module replacement or professional ECU repair services.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Komatsu service manual for your specific machine serial number. Complex electrical diagnostics should be performed by certified Komatsu technicians with proper diagnostic equipment to avoid further damage to control systems.