What is Hitachi Excavator Fault Code U2106?

Fault Code U2106 indicates a CAN communication error between the engine ECM (Engine Control Module) and the machine's main controller or display unit. This is a network communication fault specific to Hitachi excavators, signaling that critical data transmission between control modules has been interrupted or lost.

This code triggers when the Controller Area Network (CAN) bus fails to maintain proper signal exchange between the engine management system and the machine's central processor. The CAN bus acts as the digital nervous system of modern excavators, allowing various electronic modules to share sensor data, operational commands, and diagnostic information in real-time. When U2106 appears, the machine's integrated systems cannot properly coordinate, potentially affecting engine performance monitoring, hydraulic system optimization, and operator display functions. For used Hitachi excavators, this communication breakdown is critical because it can mask other underlying issues and prevent accurate diagnostics of the entire machine.

Common Symptoms

• Warning lights illuminate on the instrument cluster, particularly the engine malfunction or communications error indicator
• Loss of engine data on the monitor display—RPM, coolant temperature, or fuel level readings may freeze or show dashes
• Reduced engine power or derate mode activation as a protective measure when the ECM cannot communicate operating parameters
• Erratic gauge behavior with needles jumping or digital displays flickering intermittently
• Inability to access diagnostic data through the machine's onboard display system

Potential Causes

The most common technical failures causing U2106 in used Hitachi excavators include:

• Damaged CAN bus wiring harness, particularly at flex points near the engine mount, cab pivot areas, or along the boom where cables experience constant movement and vibration
• Corroded or loose connector pins at the ECM, main controller, or junction boxes—moisture intrusion is especially common in older machines
• Failed termination resistors on the CAN network (typically 120-ohm resistors at network endpoints)
• ECM or main controller internal failure, though less common than wiring issues in used equipment
• Voltage supply problems to either control module, often caused by failing relays, poor ground connections, or battery/charging system degradation
• Aftermarket component interference from improperly installed accessories that share the CAN network

How to Troubleshoot and Fix Code U2106

Step 1: Visual Inspection of CAN Bus Harness Begin with a thorough physical examination of the CAN communication wiring between the engine ECM and main controller. On used excavators, focus on known wear points: where harnesses pass through the cab firewall, around rotating joints, and near heat sources like exhaust components. Look for abraded insulation, pinched wires, or evidence of previous repairs with electrical tape. Check all connector bodies for corrosion, bent pins, or moisture—clean contacts with electrical contact cleaner and apply dielectric grease.

Step 2: Test CAN Bus Electrical Integrity Using a digital multimeter, measure the resistance between the CAN-High and CAN-Low wires at the network termination points—you should read approximately 60 ohms with both modules connected (two 120-ohm resistors in parallel). Disconnect one module at a time and verify each termination resistor reads 120 ohms individually. Check for short circuits to ground on both CAN wires (should show infinite resistance). Inspect supply voltage to both the ECM and main controller; verify each receives proper battery voltage (typically 24V for Hitachi equipment) and has solid ground connections with less than 0.1V drop.

Step 3: Advanced Diagnostics and Component Testing Connect Hitachi diagnostic software (Dr.EX or equivalent dealer-level software) to isolate which module is failing to communicate. The software can monitor real-time CAN traffic and identify whether the ECM is transmitting but the controller isn't receiving (or vice versa). For used machines, pay special attention to previous repair history—aftermarket harnesses or non-OEM components frequently cause communication issues. If wiring and termination resistors test correctly, perform a controller power reset by disconnecting batteries for 10 minutes. If the fault persists after these checks, suspect internal failure of either the ECM or main controller module—these require professional-grade diagnostic equipment to confirm before replacement.

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Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the manufacturer's official service manual for your specific machine model and serial number. Complex electrical diagnostics may require dealer-level diagnostic tools and trained professionals to prevent further damage or safety hazards.