Hitachi ZX870H-3 Fault Code 11402-3: Complete Diagnostic Guide

What is Hitachi ZX870H-3 Fault Code 11402-3?

Fault Code 11402-3 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 is part of Hitachi's proprietary diagnostic system for the ZX870H-3 excavator, which typically features an Isuzu engine with advanced electronic controls. The CAN bus network serves as the central nervous system for this machine, enabling critical data exchange between the ECM, hydraulic controllers, and display monitors. When communication breaks down, the excavator cannot properly coordinate engine performance with hydraulic demands, potentially causing operational inefficiencies and safety concerns.

For a machine of this size and complexity, maintaining reliable ECM communication is essential for optimal fuel efficiency, emissions control, and preventing costly component damage.

Common Symptoms

• Warning lights illuminated on the operator display, including check engine or communication error indicators
• Intermittent loss of dashboard data, such as engine RPM, temperature readings, or hydraulic pressure displays going blank
• Reduced engine power or derate mode activation, limiting machine performance to protect components
• Erratic hydraulic response or delayed reaction to joystick inputs due to coordination failures
• Difficulty starting or unexpected engine shutdowns during operation

Potential Causes

• Damaged or corroded CAN bus wiring harness, particularly at flex points near the engine mount or cab pivot areas common in used excavators
• Loose or oxidized connector pins at the ECM, instrument cluster, or junction boxes
• Failed termination resistors on the CAN network (typically 120-ohm resistors at network endpoints)
• ECM internal failure or corrupted software, more common in high-hour machines
• Voltage supply issues to the ECM caused by failing batteries, alternator problems, or poor ground connections
• Water intrusion into harness connectors from damaged seals or cab leaks
• Previous repair damage where harnesses were pinched, improperly routed, or connectors not fully seated

How to Troubleshoot and Fix Code 11402-3

Step 1: Visual Inspection Begin with a thorough physical examination of all wiring harnesses between the ECM (located near the engine) and the cab. On used excavators, pay special attention to harness routing through the swing bearing area and along the boom base where vibration and flexing cause wear. Check all connectors for corrosion, bent pins, or moisture. Clean contacts with electrical contact cleaner and apply dielectric grease.

Step 2: Electrical Testing Using a digital multimeter, verify proper voltage supply to the ECM (typically 24V on this model). Check for voltage drops exceeding 0.5V, indicating resistance in power or ground circuits. Measure CAN bus resistance between CAN-High and CAN-Low terminals at the ECM connector with the system powered off—you should read approximately 60 ohms (two 120-ohm termination resistors in parallel). Readings significantly higher suggest open circuits or missing terminators.

Step 3: Advanced Diagnostics Connect Hitachi Dr.EX diagnostic software or compatible scan tool to read live CAN bus data and pinpoint which module is failing to communicate. Monitor signal voltage on CAN-High (should be ~3.5V) and CAN-Low (should be ~1.5V) during operation. Significant deviations indicate wiring faults or controller failures.

Step 4: Component Replacement If diagnostics isolate a specific harness section, replace rather than repair spliced wiring. For ECM replacement on used machines, ensure proper programming and calibration with OEM software. Always verify the fix by clearing codes and performing a complete operational test under load.

---

Disclaimer: This guide provides general diagnostic information. Complex electrical issues may require consultation with certified Hitachi technicians or authorized service centers with specialized equipment.