Komatsu PC650-8R Fault Code DA2RMC: Complete Diagnostic Guide

What is Komatsu PC650-8R 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 PC650-8R 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 PC650-8R 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 PC650-8R's advanced KOMTRAX Plus system, which depends on seamless module integration.

Common Symptoms

When fault code DA2RMC is active, operators typically experience:

• Engine derate mode activated, limiting maximum RPM to approximately 1,500-1,800 RPM
• Amber or red warning lights illuminated on the monitor panel with communication error messages
• Sluggish hydraulic response or inconsistent boom/arm/bucket movements
• Intermittent loss of power during combined operations (swing + lift)
• Monitor display freezing or showing incomplete machine data

Potential Causes

The most common technical causes for DA2RMC on used PC650-8R excavators include:

• CAN bus wiring harness damage at known rub points near the engine mounting brackets and 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 resistors on the CAN bus network (120-ohm resistors at network endpoints)
• ECM or HCM internal failure due to moisture intrusion or age-related component degradation
• Voltage supply issues from the main power harness affecting module operation (typically 24V systems)
• Aftermarket modifications or improper repairs disrupting CAN bus integrity

How to Troubleshoot and Fix Code DA2RMC

Step 1: Visual Inspection Begin by inspecting all wiring harnesses between the ECM and HCM. On used excavators, check for harness wear at pivot points, especially where cables route near the engine and hydraulic tank. Look for chafed insulation, pinched wires, or oil contamination on connectors. Clean all connector pins with electrical contact cleaner and verify secure connections.

Step 2: CAN Bus Resistance Testing Using a digital multimeter, disconnect both ECM and HCM connectors. Measure resistance between CAN-High and CAN-Low terminals (typically pins identified in the service manual). You should read approximately 60 ohms with both modules disconnected, indicating proper termination resistors. Any reading significantly higher suggests an open circuit or failed resistor.

Step 3: Voltage and Signal Verification With the ignition on (engine off), verify 24V supply voltage at both the ECM and HCM power pins. Use Komatsu KTEC diagnostic software or compatible scan tool to monitor live CAN bus communication. Check for intermittent dropouts by wiggling harnesses while monitoring. Replace any harness sections showing signal interruption.

Step 4: Module Testing If wiring checks pass, perform ECM and HCM self-diagnostics through the service software. For used machines, moisture damage is common—inspect module housings for corrosion or water stains. Consider testing modules in a known-good machine if available before replacement.

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Disclaimer: This guide provides general diagnostic procedures for the Komatsu PC650-8R. Always consult the official Komatsu service manual and consider professional technician assistance for complex electrical diagnostics. Improper repairs may cause additional system damage.