Komatsu Fault Code E446: Complete Diagnostic Guide

What is Komatsu Fault Code E446?

Komatsu Fault Code E446 indicates a malfunction in the Engine Control Module (ECM) communication circuit, specifically a CAN bus communication error between the engine ECM and the monitor/display system. This fault triggers when the main controller loses reliable data transmission from the engine's electronic control unit, preventing proper system monitoring and coordination.

This code is critical for Komatsu excavators because the CAN (Controller Area Network) bus serves as the central nervous system, allowing the ECM, pump controller, and monitor panel to share real-time operational data. When communication fails, the machine cannot properly regulate engine output, hydraulic flow, or display accurate diagnostic information—potentially leading to reduced performance, safety risks, and difficulty diagnosing secondary issues.

Common Symptoms

When Code E446 is active, operators typically experience:

• Intermittent or complete loss of engine parameter display (RPM, temperature, fuel level) on the monitor panel
• Warning lights illuminating without clear explanation or multiple codes appearing simultaneously
• Engine derating or reduced power output as the ECM enters failsafe mode
• Erratic gauge behavior, including needles jumping or freezing on the instrument cluster
• Difficulty starting or rough idle due to improper fuel/timing adjustments from lost communication

Potential Causes

The most common technical causes for E446 in used Komatsu excavators include:

• Corroded or damaged CAN bus wiring harness, particularly at flex points near the engine mount or through bulkhead connectors
• Loose or corroded ground connections affecting ECM communication circuits (common in high-hour machines)
• Failed termination resistors on the CAN network (typically 120-ohm resistors at network endpoints)
• ECM or monitor controller internal failure, often from voltage spikes or moisture intrusion in older units
• Damaged harness from rodent activity or rubbing against frame components during operation
• Poor aftermarket repair splices in the communication wiring from previous fixes

How to Troubleshoot and Fix Code E446

Step 1: Visual Inspection of Harness and Connectors

Begin by physically inspecting the entire CAN bus wiring harness from the ECM (typically mounted on the engine or near the battery box) to the monitor panel. Look specifically for:

• Cracked or abraded wire insulation at movement points
• Green corrosion on connector pins (use electrical contact cleaner)
• Loose connector locks or spread terminals
• Evidence of previous repairs or electrical tape

On used excavators, check where harnesses pass through the cab firewall and along the engine valley—these are notorious rub points.

Step 2: Measure CAN Bus Resistance and Voltage

Using a digital multimeter, disconnect both ECM and monitor connectors. Measure resistance between the CAN High and CAN Low wires (usually twisted pair, often yellow and green on Komatsu). You should read approximately 60 ohms with both termination resistors in place, or 120 ohms at each individual terminator.

With the key on (engine off), measure voltage between CAN High and CAN Low—you should see approximately 2.5 volts DC as the resting differential voltage. Significant deviation indicates a short to power or ground.

Step 3: Check Ground Circuits and Power Supply

Verify the ECM ground connections have less than 0.1 ohms resistance to chassis ground. Clean and retighten all ground bolts. Check that the ECM receives proper voltage (typically 24V DC on Komatsu machines) with key on.

Step 4: Advanced Diagnostics with Komatsu Software

Connect Komatsu diagnostic software (KOMTRAX Plus or dealer-level tools) to monitor live CAN bus traffic. This reveals whether communication loss is intermittent or constant, and identifies which module isn't responding.

For used machinery, perform a wiggle test—gently flex harnesses while monitoring for communication dropouts, which pinpoints mechanical connection issues.

Step 5: Component Replacement

If diagnostics isolate the fault to a specific component, replace in this order: connectors first (often the cheapest fix on older machines), then wiring harness sections, and finally the ECM or monitor controller as last resort.

Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu service manual for your specific model and serial number. Complex electrical issues may require professional diagnosis with manufacturer-specific equipment.