Komatsu PC750LC-7 Fault Code DA2RMC: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code DA2RMC?

Fault Code DA2RMC indicates a communication error between the machine's Engine Control Module (ECM) and the Hydraulic Control Module (HCM) on the Komatsu PC750LC-7 excavator. This code specifically signals that the CAN bus communication network has detected an intermittent or complete loss of data transmission between these critical control systems.

The PC750LC-7 relies on continuous communication between the ECM and HCM to coordinate engine power output with hydraulic demand. When this communication fails, the machine cannot properly match engine speed to hydraulic load requirements, resulting in reduced operational efficiency and potential safety concerns. This is particularly critical in the PC750LC-7's advanced CLSS (Closed-Center Load Sensing System), which requires real-time data exchange for optimal performance.

Common Symptoms

When fault code DA2RMC is active, operators typically experience:

• Warning light illumination on the monitor panel with reduced machine performance
• Engine derating or failure to respond properly to throttle inputs
• Sluggish hydraulic response or inconsistent boom/arm/bucket movements
• Intermittent loss of power during combined operations (swing and lift simultaneously)
• Monitor display errors showing communication failure messages or blank screens

Potential Causes

The most common technical causes for DA2RMC on used PC750LC-7 excavators include:

• Corroded or damaged CAN bus connectors between ECM and HCM (especially connector X203 near the battery box)
• Harness chafing at known rub points along the right-hand frame rail where wiring passes near hydraulic lines
• Failed termination resistors in the CAN network (120-ohm resistors at network endpoints)
• ECM or HCM internal failure due to moisture intrusion or age-related component degradation
• Low battery voltage or poor ground connections affecting module power supply
• Aftermarket monitor installations that improperly tap into the CAN network

How to Troubleshoot and Fix Code DA2RMC

Step 1: Visual Inspection Begin by inspecting all wiring harnesses between the ECM (located behind the operator's cab) and HCM (mounted near the hydraulic pumps). On used excavators, pay special attention to areas where harnesses contact metal surfaces or hydraulic lines. Check connectors X203, X204, and X301 for corrosion, bent pins, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, verify battery voltage is above 24V (for 24V systems). Check CAN-High and CAN-Low wire resistance between ECM and HCM—should read approximately 60 ohms with both modules connected (indicating proper 120-ohm termination at each end). Inspect ground connections at G201 and ensure resistance to chassis is below 0.5 ohms.

Step 3: Advanced Diagnostics Connect Komatsu KOMTRAX or compatible diagnostic software to read real-time CAN bus traffic. Monitor for intermittent dropouts during machine operation. If communication is completely absent, disconnect one module at a time to isolate a potential short circuit. For used machines, replace termination resistors first (common failure point) before condemning expensive modules.

Step 4: Harness Repair If chafing or damage is found, repair using OEM-spec shielded CAN cable and apply protective sleeving. Ensure proper routing away from heat sources and moving components.

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Disclaimer: This guide provides general troubleshooting information. Complex electrical diagnostics should be performed by qualified technicians with proper training and equipment. Always consult the official Komatsu service manual for your specific machine serial number before performing repairs.