Hitachi Excavator Fault Code 119870: Complete Diagnostic Guide

What is Hitachi Fault Code 119870?

Fault Code 119870 on Hitachi excavators indicates a communication error between the Engine Control Module (ECM) and the Machine Control Unit (MCU), specifically related to CAN bus data transmission failure. This diagnostic trouble code (DTC) triggers when the engine controller cannot properly communicate with the machine's main computer system over the Controller Area Network (CAN) for longer than the calibrated timeout period.

This communication link is critical for Hitachi excavators because the ECM and MCU must constantly exchange data about engine performance, hydraulic demands, and operator inputs. When this connection fails, the machine cannot properly coordinate engine speed with hydraulic output, resulting in reduced efficiency and potential safety concerns. In used excavators, this code frequently indicates degraded wiring or connector corrosion rather than controller failure.

Common Symptoms

When Code 119870 is active, operators typically experience:

• Engine derate mode – reduced power output with engine speed limited to approximately 1,500 RPM
• Intermittent or complete loss of hydraulic function as the MCU cannot request proper engine response
• Dashboard warning lights including the check engine light and communication error indicator
• Erratic throttle response or failure of auto-idle/auto-acceleration features
• Diagnostic monitor displays showing multiple simultaneous codes due to cascading communication failures

Potential Causes

The most common technical causes for this fault code include:

• CAN bus wiring damage – particularly at harness routing points near the engine mount where vibration causes wire chafing
• Corroded or moisture-contaminated connectors at the ECM or MCU (extremely common in used machines operating in wet conditions)
• Failed termination resistors on the CAN network (120-ohm resistors at each end of the bus)
• ECM or MCU ground circuit issues creating voltage reference problems
• Software version mismatch between ECM and MCU after previous repairs or component replacement
• Physical damage to controllers from water intrusion, especially in high-hour used excavators

How to Troubleshoot and Fix Code 119870

Step 1: Visual Inspection and Connector Check

Begin by inspecting all CAN bus harness routing from the ECM (typically mounted on the engine) to the MCU (usually in the cab area). Look specifically for wire abrasion at harness supports, engine mounts, and bulkhead pass-throughs. Remove and inspect all connectors on both controllers for corrosion, bent pins, or moisture. On used excavators, check for evidence of previous repair attempts like electrical tape or non-OEM connectors, which often indicate recurring issues.

Step 2: Electrical Testing with Diagnostic Tools

Using a digital multimeter, measure CAN bus resistance between CAN-High and CAN-Low terminals with all controllers connected and ignition off. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). A reading of 120 ohms indicates one missing terminator; open circuit suggests wiring break. With ignition on, measure CAN-High and CAN-Low voltages relative to ground – you should see approximately 2.5V on each line at rest, with small fluctuations during communication.

Step 3: Advanced Diagnostics and Component Testing

Connect Hitachi Dr.EX diagnostic software or equivalent scan tool to monitor live CAN bus traffic. Observe whether the ECM is transmitting but the MCU isn't receiving (or vice versa) to isolate the faulty controller. Check for intermittent connections by wiggling harnesses while monitoring communication status. For used excavators with high operating hours, carefully inspect harness grommets where wires pass through sheet metal – these commonly wear through insulation. If all wiring and connections test properly, verify both controllers have compatible software versions using the diagnostic software.

Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the official Hitachi service manual for your specific model and serial number. If you're unfamiliar with electrical diagnostics or working with construction equipment, contact a certified Hitachi technician to prevent further damage or safety hazards.