Komatsu PC450-8 Fault Code DW91KB: Complete Diagnostic Guide

What is Komatsu PC450-8 Fault Code DW91KB?

Fault Code DW91KB indicates a communication error or abnormal signal detected in the machine monitoring system's data transmission network, specifically related to the controller area network (CAN) communication between the engine controller (ECM) and the machine controller.

This diagnostic trouble code (DTC) appears when the ECM fails to receive proper signals from connected control modules or when data packet transmission is interrupted on the CAN bus system. For the PC450-8 model, this communication network is critical because it coordinates engine performance, hydraulic functions, and operator display information. When this code activates, the machine may enter a protective derate mode to prevent potential damage from uncoordinated system operations.

Common Symptoms

When DW91KB is active on your Komatsu PC450-8, operators typically experience:

• Warning lamp illumination on the monitor panel with reduced engine power output
• Erratic gauge readings or complete loss of display information on the multi-function monitor
• Intermittent loss of hydraulic responsiveness or inconsistent attachment control
• Engine derate limiting maximum RPM to approximately 1,500-1,800 range
• Stored fault codes that may appear and disappear intermittently during operation

Potential Causes

The most common technical causes for DW91KB on used PC450-8 excavators include:

• Corroded or damaged CAN bus connectors at the ECM or machine controller harness connections (common failure point behind the operator cab)
• Harness chafing or wire breaks in the main wiring loom near the swing bearing area where repeated rotation causes wear
• Faulty termination resistors on the CAN network (120-ohm resistors that may fail in older machines)
• ECM or machine controller internal faults due to moisture intrusion or component aging
• Low battery voltage or poor ground connections affecting controller power supply stability
• Aftermarket component interference from non-OEM attachments or monitoring systems

How to Troubleshoot and Fix Code DW91KB

Step 1: Initial Inspection and Data Retrieval

Connect Komatsu KOMTRAX diagnostic software or a compatible scan tool to retrieve all active and pending codes. Document freeze frame data showing operating conditions when the fault occurred. Check battery voltage—it should read 24-26V with the engine running. Inspect all ground connections at the battery, frame, and ECM mounting points for corrosion.

Step 2: CAN Bus Physical Inspection

Locate the main CAN harness connections at the ECM (typically mounted near the right-hand fuel tank) and machine controller (behind operator seat). Disconnect connectors and inspect pins for corrosion, bent terminals, or moisture. On used excavators, pay special attention to the harness routing through the swing bearing area—this is a known wear point for the PC450-8. Look for abraded insulation or exposed wires.

Step 3: Electrical Testing

Using a digital multimeter, measure CAN-High and CAN-Low resistance between the two signal wires with all controllers disconnected. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). If readings are infinite or near zero, locate the faulty termination resistor or short circuit. Check for voltage presence on CAN lines with ignition on—readings should be approximately 2.5V on each line with minimal fluctuation.

Step 4: Component Replacement and Verification

If physical inspection and electrical tests reveal damaged connectors, replace the affected harness sections using genuine Komatsu parts to ensure proper shielding. For corroded connections on used machines, clean with electrical contact cleaner and apply dielectric grease before reconnection. Clear codes, operate the machine through various functions, and monitor for code recurrence.

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Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause additional system damage.