Komatsu PC750-7 Fault Code DA2RMC: Complete Diagnostic Guide

What is Komatsu PC750-7 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 PC750-7 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 PC750-7 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 PC750-7'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:

• Engine derate mode activated, limiting maximum RPM to approximately 1,500-1,800 RPM
• Hydraulic system sluggishness or reduced cycle times across all functions
• Warning lamp illumination on the monitor panel with accompanying fault code display
• Intermittent loss of fine control during precision operations, particularly with combined movements
• Erratic engine response when transitioning between idle and working speeds

Potential Causes

The most common technical causes for DA2RMC on used PC750-7 excavators include:

• CAN bus wiring harness damage at known rub points near the engine mounting brackets and along the right-hand chassis rail
• Corroded or moisture-contaminated connectors 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 communication circuit failure due to voltage spikes or age-related component degradation
• Loose or damaged ground connections at G201 (engine block ground) or G301 (frame ground)

How to Troubleshoot and Fix Code DA2RMC

Step 1: Visual Inspection Begin by inspecting the main wiring harness between the ECM and HCM. On used excavators, check for harness chafing where the bundle passes through the bulkhead near the hydraulic tank. Examine all connector pins for corrosion, bent terminals, or moisture intrusion—particularly the 38-pin ECM connector and 24-pin HCM connector.

Step 2: CAN Bus Electrical Testing Using a digital multimeter, measure CAN-High and CAN-Low resistance between the ECM and HCM. With ignition off and connectors disconnected, you should read approximately 60 ohms (two 120-ohm termination resistors in parallel). Check for short circuits to ground on both CAN lines—readings should show infinite resistance.

Step 3: Voltage and Signal Verification With the ignition on (engine off), measure voltage at the ECM power supply pins. Verify battery voltage (24V nominal) is present. Using Komatsu KOMTRAX diagnostic software or compatible scan tool, monitor live CAN bus traffic to identify whether the ECM or HCM is failing to transmit.

Step 4: Component Replacement Protocol If wiring and connections test satisfactory, suspect module failure. Before replacing expensive control modules on used equipment, verify all software updates are current and perform an ECM/HCM reset procedure by disconnecting battery power for 15 minutes. Replace the faulty module only after confirming proper power, ground, and communication circuit integrity.

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Disclaimer: This guide provides general diagnostic information. Complex electrical issues should be diagnosed by qualified technicians with access to manufacturer-specific tools and documentation. Always consult the Komatsu PC750-7 service manual for complete specifications and safety procedures.