Komatsu PC750-7 Fault Code E98B: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code E98B?

Fault Code E98B indicates a malfunction in the engine control system's communication circuit, specifically related to the CAN (Controller Area Network) bus communication error between the engine ECM (Engine Control Module) and other control modules.

This code triggers when the engine ECM detects abnormal or interrupted data transmission on the CAN bus network. The CAN bus is the critical communication backbone that allows the engine controller, hydraulic controller, and monitor panel to exchange real-time operational data. On the PC750-7, this communication failure can compromise engine performance monitoring, hydraulic system coordination, and operator interface functionality. Given this machine's reliance on integrated electronic controls for optimal fuel efficiency and power management, addressing E98B promptly is essential to prevent operational inefficiencies and potential secondary system failures.

Common Symptoms

• Warning lamp illumination on the monitor panel with reduced engine power output (derate mode)
• Intermittent or complete loss of monitor display data (engine RPM, temperatures, pressures showing erratic readings or blanking out)
• Hydraulic system irregularities including inconsistent swing speed or boom response due to communication loss between controllers
• Engine may enter limp mode, limiting maximum RPM to approximately 1,500-1,800 to protect components
• Multiple fault codes appearing simultaneously as other modules lose communication with the engine ECM

Potential Causes

• CAN bus wiring harness damage from abrasion at common rub points near the engine mounting brackets or along the right-hand chassis rail (known wear area on PC750-7 models)
• Corroded or loose connector pins at the ECM harness connector (C201) or junction box connections, particularly in machines operating in high-moisture environments
• Failed termination resistor on the CAN bus network (120-ohm resistor failure disrupts signal integrity)
• ECM internal failure or corrupted software, more common in high-hour used machines (8,000+ hours)
• Voltage supply issues to the ECM from the main power relay or damaged power supply wiring
• Aftermarket component interference from improperly installed accessories tapping into the electrical system

How to Troubleshoot and Fix Code E98B

Step 1: Visual Inspection and Connector Check Begin with a thorough physical inspection of the CAN bus harness routing from the engine ECM (located behind the operator cab, right side) to the main junction box. On used excavators, pay special attention to harness sections crossing the engine mount area where vibration causes insulation wear. Disconnect and inspect connector C201 at the ECM—look for green corrosion, bent pins, or moisture intrusion. Clean contacts with electrical contact cleaner and apply dielectric grease before reconnection.

Step 2: CAN Bus Continuity and Resistance Testing Using a digital multimeter, measure resistance between CAN-High and CAN-Low terminals at the ECM connector with all modules disconnected. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). A reading of 120 ohms indicates one failed terminator; infinite resistance suggests an open circuit in the wiring. Check continuity of individual CAN-High and CAN-Low wires from ECM to hydraulic controller and monitor—repair or replace damaged sections.

Step 3: Voltage Supply and ECM Verification Verify the ECM receives proper battery voltage (24V nominal) at the power supply pins with ignition on. Check for voltage drops exceeding 0.5V indicating poor ground connections. If wiring and power supply test normal, connect Komatsu KOMTRAX diagnostic software or compatible scan tool to check for ECM internal faults and verify communication with other modules. Update ECM software if outdated versions are detected. If communication remains failed with known-good wiring, ECM replacement may be necessary—source quality remanufactured units for used equipment cost-effectiveness.

Disclaimer: This guide provides general diagnostic information. Complex electrical issues may require consultation with certified Komatsu technicians or authorized service centers with model-specific diagnostic equipment. Always follow proper lockout/tagout procedures when performing electrical diagnostics.