What is Hitachi General Fault Code 11958-4?

Fault Code 11958-4 on Hitachi excavators indicates a CAN (Controller Area Network) communication error, specifically a message timeout or data loss between the engine ECM (Engine Control Module) and the machine's main controller. This diagnostic trouble code triggers when the communication bus fails to receive expected data packets within the predetermined time frame, typically measured in milliseconds.

This fault directly impacts the CAN bus system, which serves as the digital nervous system connecting all electronic control units throughout the excavator. The CAN protocol enables real-time data exchange between the engine controller, hydraulic management system, and operator display. For Hitachi excavators, maintaining uninterrupted CAN communication is critical because the machine relies on coordinated signals to manage fuel injection timing, hydraulic flow rates, and safety interlocks. When this communication breaks down, the machine may enter a protective derate mode to prevent potential damage from unsynchronized systems.

Common Symptoms

• Warning lights: The check engine lamp and/or master caution light illuminate on the instrument cluster, often accompanied by error messages on digital displays
• Performance derate: Engine power limitation (typically 25-40% reduction) or complete shutdown in severe cases, preventing normal operation
• Intermittent communication loss: Gauges may freeze, flicker, or display erratic readings including engine RPM, coolant temperature, or hydraulic oil temperature
• Hydraulic system irregularities: Sluggish or unresponsive hydraulic functions due to loss of coordinated control signals between systems
• Diagnostic software connection failures: Difficulty establishing stable connections with service tools when attempting system diagnostics

Potential Causes

The CAN bus harness in used Hitachi excavators commonly experiences wear at pivot points, particularly near the cabin base and boom connection areas where repetitive flexing occurs. Inspect these high-stress zones first.

Corroded or loose connector pins at the ECM, main controller, or junction boxes disrupt signal integrity. Used machines exposed to moisture or salt environments show accelerated connector degradation.

Faulty terminating resistors at CAN bus endpoints (typically 120-ohm resistors) can fail over time, causing signal reflection and data corruption.

ECM or controller module failure, while less common, occurs in high-hour machines where internal capacitors degrade or circuit boards develop micro-cracks from vibration.

Aftermarket accessories or improperly installed telematics devices may create electrical interference or improper bus loading on the CAN network.

How to Troubleshoot and Fix Code 11958-4

Step 1: Visual Harness Inspection Begin with a thorough physical examination of all CAN bus wiring from the engine ECM to the main controller. On used excavators, focus on areas where harnesses route through moving components or contact metal surfaces. Look for abraded insulation, pinched wires, or evidence of rodent damage. Check all connector boots for cracks that allow moisture intrusion.

Step 2: Connector and Termination Resistance Testing Disconnect battery power before inspecting connectors. Clean all CAN-High and CAN-Low terminals with electrical contact cleaner and verify pin tension. Using a digital multimeter, measure resistance between CAN-High and CAN-Low lines with all modules disconnected—you should read approximately 60 ohms if both 120-ohm terminating resistors are intact. Readings significantly higher indicate an open terminating resistor.

Step 3: Live Signal Verification Reconnect the system and use Hitachi diagnostic software (Dr.EX or equivalent) or a specialized CAN bus analyzer to monitor real-time communication. Observe for message dropouts, error frames, or abnormal bus voltage levels. Proper CAN-High voltage should read approximately 3.5V while CAN-Low reads 1.5V during active communication (2.5V differential). Significant deviation indicates wiring issues or module faults.

Step 4: Module Isolation Testing If harness and termination checks pass, systematically disconnect non-essential CAN-connected modules one at a time to identify if a specific controller is corrupting the bus. A faulty module may continuously transmit error frames or fail to properly acknowledge messages.

For used excavators, replace suspect harness sections rather than attempting repairs, as patched wiring rarely provides long-term reliability in high-vibration environments.

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Disclaimer: This guide provides general troubleshooting information for Fault Code 11958-4. Always consult the official Hitachi service manual for your specific model and serial number. Complex electrical diagnostics should be performed by qualified technicians with appropriate diagnostic equipment. Improper repairs to CAN bus systems may result in additional control module damage.