Hitachi ZX870H-3 Fault Code 11404-3: Complete Diagnostic Guide

What is Hitachi ZX870H-3 Fault Code 11404-3?

Fault Code 11404-3 indicates a malfunction in the Engine Control Module (ECM) communication circuit, specifically related to CAN (Controller Area Network) bus communication errors or data transmission failures between the engine controller and other machine systems.

This code triggers when the ECM detects inconsistent, interrupted, or absent communication signals on the CAN bus network. For the ZX870H-3, this is critical because the CAN system coordinates data between the engine management system, hydraulic controllers, and display monitors. Communication failures can result in reduced machine performance, inaccurate sensor readings, or complete system shutdowns, making immediate diagnosis essential for operational safety and productivity.

Common Symptoms

When Code 11404-3 is active, operators typically experience:

• Warning lights illuminated on the instrument cluster, particularly the engine malfunction or communication error indicators
• Intermittent or complete loss of dashboard display information (engine RPM, temperature, pressure readings)
• Erratic engine behavior including unexpected derating, rough idling, or failure to respond to throttle inputs
• Hydraulic system irregularities due to loss of coordinated control between engine and hydraulic ECUs
• Multiple fault codes appearing simultaneously as various controllers lose communication capability

Potential Causes

The most common technical causes for this fault code in used ZX870H-3 excavators include:

• CAN bus wiring harness damage from abrasion, particularly at flex points near the engine bay or along the boom structure
• Corroded or loose connector pins at the ECM, junction boxes, or termination resistors due to moisture intrusion
• Failed termination resistors (120-ohm) at CAN bus endpoints causing signal reflection and data corruption
• ECM internal failure or corrupted firmware, more common in high-hour machines
• Voltage supply issues to the CAN network from damaged power distribution circuits or poor grounding points
• Physical damage to controllers from vibration, impact, or water ingress in used equipment

How to Troubleshoot and Fix Code 11404-3

Step 1: Visual Inspection Begin with a thorough physical examination of all CAN bus harness routing. On used excavators, check known wear points where harnesses contact frame members, especially near the engine mount and along the right-side chassis rail. Inspect all connector terminals for corrosion, bent pins, or moisture. Clean connections with electrical contact cleaner and apply dielectric grease.

Step 2: Electrical Testing Using a digital multimeter, measure CAN-High and CAN-Low voltage at the ECM connector with ignition on, engine off. You should read approximately 2.5V on each line at rest. Check termination resistance by disconnecting both ends of the CAN bus and measuring between CAN-H and CAN-L terminals—expect 60 ohms (two 120-ohm resistors in parallel). Deviations indicate open circuits or failed resistors.

Step 3: Advanced Diagnostics Connect Hitachi Dr.EX diagnostic software or compatible scan tool to monitor real-time CAN bus traffic and identify which controller is dropping communication. Check ECM power supply voltage (should be 24V nominal) and verify clean chassis ground connections at the ECM mounting location. For used machines, remove and inspect ECM connectors for "green corrosion" on pins—a common failure point requiring connector replacement.

Step 4: Component Replacement If diagnostics isolate a specific failed component, replace the wiring harness section, termination resistor, or ECM as needed. Always verify proper CAN bus operation after repairs by clearing codes and performing a complete machine function test.

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Disclaimer: This guide provides general diagnostic information. Complex electrical issues should be diagnosed by qualified technicians with proper Hitachi diagnostic equipment. Always consult the official service manual and follow safety protocols when working on heavy equipment electrical systems.