Komatsu PC400-8 Fault Code E0EDA2RMC: Complete Diagnostic Guide

What is Komatsu PC400-8 Fault Code E0EDA2RMC?

Fault Code E0EDA2RMC indicates a communication error between the Engine Control Module (ECM) and the Hydraulic Control Module (HCM) on the Komatsu PC400-8 excavator. This code specifically relates to the CAN bus communication network that allows these critical control systems to exchange operational data.

This fault affects the integrated control system that manages engine performance relative to hydraulic demand. The PC400-8 uses sophisticated load-sensing technology where the ECM and HCM must communicate continuously to optimize fuel efficiency and hydraulic response. When this communication fails, the machine cannot properly coordinate engine output with hydraulic requirements, potentially leading to reduced performance and increased fuel consumption.

Common Symptoms

When Code E0EDA2RMC is active, operators typically experience:

• Warning light illumination on the monitor panel, often accompanied by a communication error message
• Reduced hydraulic response or sluggish boom/arm movements due to improper engine-hydraulic coordination
• Engine derate mode where maximum RPM is limited to protect the powertrain
• Intermittent loss of monitor display functions, including loss of real-time operational data
• Increased fuel consumption as the system defaults to non-optimized operating parameters

Potential Causes

The most common technical causes for this fault code include:

• CAN bus wiring harness damage between the ECM and HCM, particularly at known rub points near the engine mounting brackets and along the main chassis harness
• Corroded or loose connector pins at the ECM or HCM connection points—especially common in used excavators exposed to moisture
• Failed termination resistors on the CAN bus network (120-ohm resistors at network endpoints)
• ECM or HCM internal communication circuit failure, though less common than wiring issues
• Voltage supply problems to either control module, typically caused by poor ground connections or battery issues
• Previous repair attempts where harness routing was modified, creating new wear points

How to Troubleshoot and Fix Code E0EDA2RMC

Step 1: Visual Inspection Begin with a thorough inspection of the wiring harness between the ECM (located behind the operator cab) and the HCM (mounted near the hydraulic pump). On used excavators, pay special attention to harness routing near the engine mounts and swing bearing area where vibration causes wear. Check all connector pins for corrosion, bent terminals, or moisture intrusion.

Step 2: CAN Bus Resistance Testing Using a digital multimeter, disconnect both the ECM and HCM connectors. Measure resistance across the CAN-High and CAN-Low terminals. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). A reading significantly higher suggests an open circuit; lower readings may indicate a short to ground.

Step 3: Voltage and Signal Testing With the key in the ON position (engine off), verify battery voltage (12-14V) is present at both control modules. Using Komatsu KOMTRAX diagnostic software or a compatible scan tool, monitor live CAN bus communication. Check for intermittent dropouts that suggest loose connections rather than complete failures.

Step 4: Harness Continuity Check Test continuity of individual wires in the communication harness. For used machines, remove protective loom covering to inspect for chafing, rodent damage, or previous repair splices that may have failed. Replace any compromised sections with proper gauge wire and weatherproof connectors.

Step 5: Module Testing If wiring checks pass, the issue likely resides in the ECM or HCM. Swap modules with a known-good unit if available, or consult Komatsu technical support for module-specific testing procedures.

---

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 official Komatsu service manual for your specific machine serial number.