Komatsu PC800-7 Fault Code DA2RMC: Complete Diagnostic Guide

What is Komatsu PC800-7 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 PC800-7 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 PC800-7 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 fault is particularly critical because it affects the integrated control system that distinguishes modern Komatsu excavators from older mechanical models.

Common Symptoms

When DA2RMC is active, operators typically experience:

• Engine derate mode activated, limiting maximum RPM to approximately 1,500-1,800 RPM
• Amber warning light illuminated on the monitor panel with communication error message
• Sluggish hydraulic response or inconsistent boom/arm/bucket speed despite throttle input
• Intermittent loss of monitor display data showing engine parameters or hydraulic temperatures
• Reduced swing speed and overall cycle times due to power management restrictions

Potential Causes

The most common technical causes for DA2RMC on used PC800-7 excavators include:

• CAN bus wiring harness damage at known rub points near the engine mounting brackets or along the right-hand chassis 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 water intrusion
• Aftermarket component interference from non-OEM monitors or accessories tapped into the CAN network
• Low battery voltage (below 22V on 24V system) causing communication dropout during cranking

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 pass through bulkheads or near moving components. On used excavators, check for harness chafing against the engine block and frame rails—a common wear point on PC800-7 models. Inspect all connector pins for corrosion, bent terminals, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, verify battery voltage is above 24V with the engine off. Check CAN bus termination resistance by disconnecting both ECM and HCM connectors and measuring resistance between CAN-High and CAN-Low pins—you should read approximately 60 ohms (two 120-ohm resistors in parallel). Measure continuity on CAN-High and CAN-Low wires individually to confirm no opens or shorts to ground.

Step 3: Diagnostic Software Analysis Connect Komatsu KOMTRAX or compatible diagnostic software to retrieve freeze frame data and monitor live CAN bus traffic. Check for additional stored codes that might indicate the primary failure point. Monitor communication status while wiggling harnesses to identify intermittent connections—a critical step for used machinery where connector fatigue is common.

Step 4: Component Replacement If wiring and connections test good, suspect ECM or HCM failure. Before replacing expensive modules on used equipment, verify all ground connections are clean and tight, particularly the main chassis ground near the battery box. Replace any corroded connectors with OEM parts to ensure proper pin tension and sealing.

---

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnosis for complex electrical issues. Improper repairs may cause additional damage or safety hazards.