Komatsu PC220-10 Fault Code DW91KB: Complete Diagnostic Guide

What is Komatsu PC220-10 Fault Code DW91KB?

Fault Code DW91KB indicates a communication error between the Machine Control Unit (MCU) and the Engine Control Module (ECM) on the Komatsu PC220-10 excavator. This code triggers when the CAN bus network fails to transmit or receive critical data packets between these two primary control systems within the specified timeout period.

This communication fault is critical for the PC220-10's performance because the MCU relies on continuous data exchange with the ECM to coordinate hydraulic pump output, engine rpm control, and overall machine efficiency. When this link fails, the excavator cannot optimize power distribution, leading to operational restrictions and potential safety concerns. The PC220-10's advanced Komtrax system depends heavily on this communication pathway to manage fuel efficiency and monitor emissions compliance.

Common Symptoms

When fault code DW91KB is active, operators typically experience:

• Engine derate mode – Machine automatically limits engine power to 70-80% capacity to protect components
• Amber warning light illuminated on the monitor panel with accompanying fault message
• Loss of Auto-Idle functionality – Engine fails to automatically reduce rpm during neutral periods
• Hydraulic response lag – Slower cycle times due to inability to match hydraulic demand with engine output
• Monitor display errors – Engine parameters (temperature, rpm, fuel rate) may show dashes or freeze on screen

Potential Causes

The most common technical reasons for DW91KB on used PC220-10 excavators include:

• CAN bus harness damage – Known wear point where the main harness passes through the frame near the swing bearing, causing wire chafing
• Corroded or loose connectors at the ECM (located behind the operator's cab) or MCU (positioned in the electrical box)
• ECM or MCU software corruption from previous electrical surges or improper jump-starting procedures
• Failed termination resistor on the CAN network (120-ohm resistor failure common in machines with 6,000+ hours)
• Voltage irregularities from aging alternator or weak batteries affecting controller stability

How to Troubleshoot and Fix Code DW91KB

Step 1: Visual Inspection Begin by inspecting all CAN bus connectors at both the ECM and MCU. On used excavators, pay special attention to connector pins for corrosion (green/white oxidation). Clean contacts with electrical contact cleaner and apply dielectric grease. Check the harness routing along the right-hand side frame rail for abrasion points.

Step 2: CAN Bus Continuity Testing Using a digital multimeter, disconnect power and measure resistance between CAN-High and CAN-Low terminals at the ECM connector. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). A reading of 120 ohms indicates one failed terminator; infinite resistance means an open circuit in the harness.

Step 3: Voltage and Signal Testing With the ignition on (engine off), measure voltage at the CAN-High line (should read 2.5-3.5V) and CAN-Low line (should read 1.5-2.5V). Significant deviation indicates controller failure or power supply issues.

Step 4: Software Diagnostics Connect Komatsu KTEC diagnostic software to verify controller versions and check for stored freeze-frame data. Update ECM and MCU firmware if versions are mismatched, as this commonly occurs after component replacement on used machines.

Step 5: Component Replacement Priority If all tests pass but the code persists, replace components in this order: CAN termination resistors (cheapest fix), harness sections showing wear, then controllers (always replace MCU before ECM as it's more failure-prone).

Disclaimer: This guide provides general troubleshooting steps for qualified diesel technicians. Always consult the official Komatsu service manual for your specific serial number range and consider professional diagnostic services for complex electrical issues.