Komatsu PC750SE-7 Fault Code DA2RMC: Complete Diagnostic Guide

What is Komatsu PC750SE-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 PC750SE-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 PC750SE-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 on the PC750SE-7 due to its advanced load-sensing hydraulic system that requires real-time data exchange.

Common Symptoms

When DA2RMC is active, operators typically experience:

• Warning light illumination on the monitor panel with reduced machine performance
• Engine derating or failure to reach full RPM under load
• Sluggish hydraulic response or inconsistent boom/arm/bucket movements
• Intermittent loss of power that may resolve temporarily after key cycling
• Multiple secondary fault codes appearing simultaneously related to hydraulic or engine systems

Potential Causes

The most common technical causes for DA2RMC on used PC750SE-7 excavators include:

• CAN bus wiring harness damage at known rub points near the engine mounting brackets or along the right-side frame rail
• Corroded or loose connector pins at the ECM (located behind the operator cab) or HCM (mounted near the hydraulic pump)
• Failed termination resistor on the CAN bus network (120-ohm resistor failure)
• ECM or HCM internal communication circuit failure due to voltage spikes or age-related component degradation
• Contaminated electrical connectors from hydraulic oil leaks or water intrusion in the engine compartment

How to Troubleshoot and Fix Code DA2RMC

Step 1: Visual Inspection Begin by inspecting all wiring harnesses between the ECM and HCM for physical damage, particularly where harnesses contact frame members. On used excavators, check for wire insulation wear from vibration and connector corrosion from environmental exposure.

Step 2: Connector Testing Disconnect both ECM and HCM connectors. Use electrical contact cleaner and inspect pins for corrosion or bent terminals. Measure resistance between CAN-High and CAN-Low terminals (should read approximately 60 ohms with key off, indicating proper termination).

Step 3: CAN Bus Voltage Check Using a digital multimeter, measure voltage on CAN-High (typically 2.5-3.5V) and CAN-Low (typically 1.5-2.5V) with key on, engine off. Significant deviation indicates network communication failure.

Step 4: Diagnostic Software Analysis Connect Komatsu KOMTRAX or compatible diagnostic software to read real-time CAN bus traffic. Monitor for message dropout or error frame counts that indicate intermittent failures.

Step 5: Component Replacement If wiring and connectors test properly, suspect ECM or HCM failure. For used machines, verify software version compatibility between modules before replacement, as mismatched firmware can cause communication errors.

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Disclaimer: This guide provides general diagnostic information. Always consult Komatsu service manuals and qualified technicians for machine-specific procedures. Improper diagnosis may result in unnecessary part replacement or safety hazards.