Komatsu PC750LC-7 Fault Code E98B: Complete Diagnostic Guide

What is Komatsu PC750LC-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 appears when the ECM detects abnormal or interrupted data transmission across the machine's internal network. The PC750LC-7 relies on continuous communication between the engine controller, hydraulic controller, and monitor panel to optimize performance and fuel efficiency. When this communication fails, the machine cannot properly coordinate engine output with hydraulic demand, potentially causing operational inefficiencies and safety concerns.

For this specific model, the CAN bus system is critical because it manages the integration between Komatsu's SAA6D140E-3 engine and the advanced hydraulic system, ensuring proper load-sensing and power distribution.

Common Symptoms

When Code E98B is active, operators typically experience:

• Warning light illumination on the monitor panel with error message display
• Intermittent loss of monitor functions, including gauge readings or backup camera display
• Reduced engine power or unexpected derate mode activation
• Erratic hydraulic response or inconsistent swing/boom speed
• Engine shutdown in severe cases where communication is completely lost

Potential Causes

The most common technical causes for E98B on used PC750LC-7 excavators include:

• Damaged or corroded CAN bus wiring harness, particularly at flex points near the engine mount or cab pivot
• Loose or oxidized connector pins at the ECM, monitor panel, or hydraulic controller connections
• Failed termination resistor in the CAN network (120-ohm resistor failure)
• ECM internal communication circuit failure due to voltage spikes or water intrusion
• Aftermarket component interference, especially non-OEM monitors or accessories tapped into the network
• Worn harness insulation from rubbing against frame members (common failure point behind the cab)

How to Troubleshoot and Fix Code E98B

Step 1: Visual Inspection Begin by inspecting all wiring harnesses along the CAN bus network. Focus on areas where cables flex during machine operation—particularly the harness routing from the engine compartment to the cab. Look for chafed insulation, pinched wires, or evidence of rodent damage. Check all connector terminals for corrosion, bent pins, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, measure the resistance between the CAN-High and CAN-Low terminals at the ECM connector (typically pins should show 60 ohms with key off, indicating two 120-ohm termination resistors in parallel). Consult the PC750LC-7 service manual for exact pin locations. Check for voltage drops along the harness—any reading above 0.2V indicates excessive resistance from corrosion or damaged conductors.

Step 3: Diagnostic Software Analysis Connect Komatsu KOMTRAX or compatible diagnostic software to retrieve detailed fault data, including communication error frequency and which specific module is failing to respond. This pinpoints whether the issue originates from the ECM, hydraulic controller, or monitor panel.

Step 4: Component Isolation Systematically disconnect non-essential devices from the CAN network to identify if an aftermarket component is causing bus conflicts. For used excavators, previous owners may have installed third-party monitoring systems that create communication interference.

Step 5: Repair and Verification Replace damaged harness sections using OEM-spec shielded cable, ensuring proper routing away from heat sources and moving parts. Clean all connector contacts with electrical contact cleaner and apply dielectric grease. If termination resistors are faulty, replace them with exact 120-ohm, 1/4-watt specifications. After repairs, clear codes and perform a full operational test under load.

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Disclaimer: This guide provides general diagnostic information for Code E98B. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnosis for complex electrical issues. Improper repairs to CAN bus systems can cause additional control module damage.