What is Hitachi Excavator Fault Code 987-3?

Fault Code 987-3 on Hitachi excavators indicates a communication error or malfunction in the machine's CAN (Controller Area Network) bus system, specifically related to data transmission failures between the main controller and auxiliary control modules. This diagnostic trouble code (DTC) signals that the ECM (Engine Control Module) is unable to properly receive or send data packets to one or more networked components within the machine's electronic architecture.

This fault is critical because Hitachi excavators rely on continuous CAN bus communication to coordinate engine performance, hydraulic system operations, and operator interface displays. When communication breaks down, the machine may enter a protective derate mode or experience unpredictable behavior that compromises both productivity and safety on the jobsite.

Common Symptoms

When Code 987-3 is active, operators typically experience:

• Intermittent or complete loss of dashboard display functions, including gauge readings and warning indicators
• Erratic hydraulic response or sudden loss of auxiliary hydraulic functions (attachment control issues)
• Engine derate mode activation, limiting RPM and overall machine power output
• Multiple simultaneous warning lights illuminating on the instrument cluster without clear correlation
• Difficulty starting or unexpected engine shutdowns during operation

Potential Causes

The most common technical causes for Code 987-3 in used Hitachi excavators include:

• Corroded or loose CAN bus connectors, particularly at junction points exposed to moisture and vibration
• Damaged wiring harness sections where cables rub against the frame or hydraulic lines (common wear points near the swing bearing and boom cylinders)
• Failed auxiliary control module such as the hydraulic controller or display panel ECU
• Poor ground connections affecting network voltage stability
• Water intrusion into sealed connectors from damaged harness boots or failed grommets
• Aftermarket attachment installations that improperly tap into the CAN network

How to Troubleshoot and Fix Code 987-3

Step 1: Visual Inspection Begin with a thorough physical examination of all CAN bus wiring harnesses, paying special attention to high-flex areas near the operator cab, swing bearing, and engine compartment. Look for abraded insulation, pinched wires, or connectors with visible corrosion. On used excavators, check for previous repair attempts using electrical tape or non-OEM connectors that may have degraded.

Step 2: Connector and Ground Testing Disconnect and inspect each CAN bus connector along the network. Clean terminals with electrical contact cleaner and verify all pins make solid contact. Using a multimeter, test ground points for continuity and ensure resistance readings below 1 ohm. Check CAN-High and CAN-Low wire resistance between modules (should typically measure 60 ohms across the terminated network).

Step 3: Diagnostic Software Analysis Connect Hitachi diagnostic software (Dr.EX or equivalent) to isolate which specific module is failing to communicate. Monitor live CAN bus traffic to identify intermittent dropouts. Check voltage levels on CAN-High (typically 2.5-3.5V) and CAN-Low (1.5-2.5V) during operation using an oscilloscope if available.

Step 4: Component Replacement If diagnostics identify a specific failed module, replace the faulty control unit with OEM or verified compatible parts. For harness damage, repair sections using proper CAN-rated shielded cable and heat-shrink connections—avoid simple wire splicing. Always apply dielectric grease to reconnected terminals.

Disclaimer: This guide provides general troubleshooting information. Always consult Hitachi service manuals specific to your machine model and serial number. Complex electrical diagnostics should be performed by qualified technicians with proper diagnostic equipment.