What is Komatsu PC110-8M0 Fault Code DW91KB?

Fault Code DW91KB indicates a communication error between the Engine Control Module (ECM) and the Hydraulic Control Unit (HCU) on the Komatsu PC110-8M0 excavator. This code specifically signals an intermittent or complete loss of data transmission on the Controller Area Network (CAN) bus that links these critical systems.

The PC110-8M0 relies on constant communication between the ECM and HCU to optimize engine performance with hydraulic demand. When this communication fails, the machine cannot properly coordinate power delivery, leading to inefficient operation and potential component stress. This fault is particularly concerning on used excavators where wiring harnesses and connectors have endured years of vibration, moisture exposure, and temperature cycling.

Common Symptoms

• Yellow warning light illuminated on the instrument panel with reduced hydraulic responsiveness
• Engine derating to protect systems, resulting in sluggish boom and bucket movements
• Intermittent loss of auxiliary hydraulic functions during operation
• Erratic engine RPM fluctuations when operating multiple hydraulic circuits simultaneously
• Error codes stored in memory even after symptoms temporarily disappear

Potential Causes

The most common causes for Code DW91KB on used PC110-8M0 excavators include:

• Corroded or loose CAN bus connectors at the ECM or HCU locations (common failure point after 3,000+ hours)
• Damaged wiring harness near the swing bearing area where cables flex repeatedly
• Failed termination resistor on the CAN network (typically 120-ohm resistance)
• Moisture intrusion in the main harness connector behind the operator cab
• ECM or HCU internal communication module failure (less common but possible on high-hour machines)
• Voltage irregularities from failing alternator or weak battery connections affecting digital communication

How to Troubleshoot and Fix Code DW91KB

Step 1: Visual Inspection Examine all wiring harnesses between the ECM (located under the operator seat) and the HCU (mounted near the hydraulic pump). Look for abraded insulation, particularly where harnesses pass through metal grommets or near the swing bearing. Check all connectors for corrosion, bent pins, or moisture—clean with electrical contact cleaner if necessary.

Step 2: CAN Bus Resistance Check Using a digital multimeter, disconnect both the ECM and HCU connectors. Measure resistance between CAN-High and CAN-Low terminals at each end. You should read approximately 60 ohms with both modules disconnected (indicating proper 120-ohm termination resistors in parallel). Readings outside 55-65 ohms suggest wiring breaks or failed terminators.

Step 3: Power Supply Verification Verify both modules receive stable 12-24V supply voltage with the key on. Check ground connections at both the ECM and HCU mounting points—remove, clean, and retighten. Poor grounds are frequent culprits on used machines with accumulated dirt and oxidation.

Step 4: Diagnostic Software Scan Connect Komatsu KOMTRAX or compatible diagnostic software to read real-time CAN bus activity. Monitor for communication dropouts during machine operation. This identifies whether the fault is continuous or intermittent (suggesting vibration-related connection issues).

Step 5: Component Replacement If wiring and connections test properly, suspect internal module failure. On used excavators with 5,000+ hours, HCU failures are more common than ECM issues. Consider testing with a known-good unit before purchasing expensive replacements.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and seek professional diagnostic assistance for complex electrical issues. Improper repairs may cause additional damage or safety hazards.