What is Hitachi Excavator Fault Code 13991-2?

Fault Code 13991-2 on Hitachi excavators indicates an abnormal signal from the Engine Control Module (ECM) communication circuit, specifically related to a CAN (Controller Area Network) bus communication error between the engine controller and machine control systems. This diagnostic trouble code (DTC) is triggered when the ECM detects intermittent or complete loss of data transmission on the CAN communication line, preventing proper coordination between engine management and hydraulic control systems.

This code is critical for Hitachi excavators because the CAN bus serves as the nervous system of modern excavators, enabling real-time data exchange between multiple control units. When communication fails, the machine cannot properly regulate engine performance, hydraulic functions, and operator interface systems, potentially leading to unexpected behavior or complete operational shutdown.

Common Symptoms

When Code 13991-2 is active, operators typically experience:

• Dashboard warning lights illuminating, including the check engine light and potentially multiple system fault indicators simultaneously
• Reduced engine power or derate mode activation, limiting machine performance to protect components
• Erratic hydraulic response or inconsistent attachment control due to incomplete command signals
• Intermittent gauge cluster failures, with displays flickering or showing incorrect readings
• Engine starting difficulties or unexpected shutdowns, particularly after the machine has warmed up

Potential Causes

The most common technical reasons for Code 13991-2 on used Hitachi excavators include:

• CAN bus wiring harness damage from abrasion against frame components, particularly near the engine bay where vibration is highest
• Corroded or loose connector pins at ECM connections or junction points along the communication network
• Failed termination resistors at either end of the CAN bus network (typically 120-ohm resistors)
• ECM internal failure or software corruption, more common in machines with 5,000+ operating hours
• Voltage irregularities caused by weak batteries, failing alternators, or poor ground connections affecting signal integrity
• Aftermarket component interference from improperly installed accessories that disrupt CAN communication protocols

How to Troubleshoot and Fix Code 13991-2

Step 1: Visual Inspection Begin by thoroughly inspecting all wiring harnesses along the CAN bus network, focusing on areas where cables route near moving parts or sharp edges. Check for worn insulation, pinched wires, or evidence of previous repairs. On used excavators, pay special attention to connector housings for corrosion, moisture intrusion, or bent pins—clean connections with electrical contact cleaner and ensure positive locking engagement.

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 measuring between CAN-High and CAN-Low terminals with all modules disconnected—you should read approximately 60 ohms (two 120-ohm resistors in parallel). Deviations indicate open circuits or missing termination resistors.

Step 3: Advanced Diagnostics Connect Hitachi diagnostic software (Dr.EX or equivalent) to monitor real-time CAN bus activity and identify which specific module is dropping communication. Test battery voltage under load—weak electrical systems cause communication errors on used machines. Inspect ground connections at the ECM mounting points, cleaning contact surfaces to bare metal. If all wiring tests pass, the ECM itself may require replacement or reprogramming by an authorized Hitachi technician.

Disclaimer: This guide provides general troubleshooting information. Always consult the manufacturer's service manual for your specific model and consider engaging a certified Hitachi technician for complex electrical diagnostics and ECM programming procedures.