Komatsu PC750-7 Fault Code E115: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code E115?

Fault Code E115 on the Komatsu PC750-7 indicates a malfunction in the Engine Controller (ECM) communication circuit, specifically related to the CAN (Controller Area Network) communication line between the engine controller and the machine controller.

This diagnostic trouble code triggers when the ECM detects an interruption, abnormal signal, or complete loss of communication on the CAN bus network. The CAN system is critical for the PC750-7's integrated control architecture, as it enables real-time data exchange between the engine management system, hydraulic controllers, and monitoring displays. When this communication fails, the machine cannot properly coordinate engine performance with hydraulic demands, potentially causing operational inefficiencies and safety concerns.

Common Symptoms

When Code E115 is active, operators typically experience:

• Monitor display errors or complete loss of engine parameter readings (RPM, coolant temperature, fuel level)
• Warning lights illuminated on the instrument cluster, particularly the engine malfunction indicator
• Reduced engine power or derate mode activation as a protective measure
• Erratic hydraulic response due to improper engine-hydraulic coordination
• Intermittent starting issues or failure of the machine to enter normal operating mode

Potential Causes

The most common technical causes for E115 on used PC750-7 excavators include:

• CAN bus wiring harness damage from abrasion at known rub points near the engine mounting brackets or along the boom base
• Corroded or loose connector pins at the ECM or machine controller connection points (especially in machines exposed to moisture)
• Failed termination resistors on the CAN network (120-ohm resistors at network endpoints)
• ECM internal failure or corrupted firmware, more common in high-hour machines
• Voltage supply issues to controllers due to aging battery cables or poor grounding connections
• Previous repair damage to harnesses during engine or hydraulic system service

How to Troubleshoot and Fix Code E115

Step 1: Visual Inspection Begin with a thorough inspection of the CAN bus harness routing from the engine ECM (located near the engine firewall) to the machine controller. Check for pinched wires, abraded insulation, or damaged connectors. On used excavators, pay special attention to harness sections near moving components or heat sources.

Step 2: Connector and Resistance Testing Disconnect the CAN-H and CAN-L wires at both the ECM and machine controller. Using a digital multimeter, measure resistance between CAN-H and CAN-L terminals—you should read approximately 60 ohms with both termination resistors intact. Check each termination resistor individually (should read 120 ohms each). Inspect all connector pins for corrosion or bent terminals.

Step 3: Voltage and Signal Verification With ignition on (engine off), measure voltage at the ECM power supply pins—should read battery voltage (24V nominal). Using Komatsu KOMTRAX diagnostic software or compatible scan tool, monitor CAN bus activity. Look for intermittent dropouts or error frames that indicate signal integrity issues.

Step 4: Harness Repair or Replacement If wiring damage is found, repair using proper CAN-compliant twisted-pair cable and heat-shrink connections. For used machines with extensive harness wear, consider replacing the entire engine-to-cab harness section to prevent recurring failures.

Step 5: ECM Testing If all wiring tests pass, the ECM itself may require replacement or reprogramming. Verify with Komatsu technical support whether firmware updates address known E115 issues for your machine's serial number range.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC750-7 service manual and consider professional assistance from certified Komatsu technicians for complex electrical diagnostics and ECM replacement procedures.