Komatsu PC750LC-7 Fault Code DW91KA: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code DW91KA?

Fault Code DW91KA indicates a communication error or data link failure between the engine controller (ECM) and the machine monitor system on the Komatsu PC750LC-7 excavator. This code specifically relates to the CAN bus communication network that allows critical systems to exchange operational data in real-time.

The PC750LC-7 relies on continuous data transmission between its SAA6D140E-3 engine's ECM and the machine's central monitoring system to regulate performance, fuel efficiency, and emissions control. When this communication link fails, the machine cannot properly coordinate engine output with hydraulic demands, potentially causing operational inefficiencies and triggering protective derate modes.

Common Symptoms

When DW91KA is active, operators typically experience:

• Intermittent or complete loss of engine data on the monitor display (RPM, coolant temperature, fuel level showing dashes or zeros)
• Warning lights illuminating on the instrument cluster, particularly the engine malfunction indicator
• Reduced engine power or derate mode activation as a protective measure
• Erratic gauge behavior with needles fluctuating or freezing unexpectedly
• Inability to access diagnostic information through the standard monitor interface

Potential Causes

The most common technical causes for DW91KA on used PC750LC-7 excavators include:

• Corroded or damaged CAN bus connectors at the ECM or monitor harness junction points
• Wiring harness chafing along the right-hand frame rail where cables route near hydraulic lines (known wear point on this model)
• Failed termination resistors in the CAN network causing signal reflection
• ECM or monitor controller internal failure due to moisture intrusion or age-related component degradation
• Loose or oxidized ground connections affecting communication voltage reference
• Aftermarket component interference from non-OEM radios or accessories tapped into the electrical system

How to Troubleshoot and Fix Code DW91KA

Step 1: Visual Inspection Begin by thoroughly inspecting all wiring harnesses between the engine ECM (located on the right side of the engine) and the cab monitor. On used excavators, pay special attention to harness routing near the hydraulic pump and along the swing bearing area where vibration causes insulation wear. Check all connector pins for corrosion, bent terminals, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, verify CAN-High and CAN-Low voltage levels at the ECM connector. You should measure approximately 2.5V on each line with the key on, engine off. Check for 120-ohm resistance between CAN-High and CAN-Low terminals with the system powered down—this confirms proper termination. Resistance significantly higher suggests open circuits or failed terminators.

Step 3: Advanced Diagnostics Connect Komatsu KOMTRAX or compatible diagnostic software to isolate whether the fault originates from the ECM or monitor side. Monitor live data streams while wiggling suspect harness sections to identify intermittent connections. For used machines, inspect the main ground strap from the engine block to the frame for corrosion—clean and re-torque to specification (typically 40-50 ft-lbs).

Step 4: Component Replacement If diagnostics isolate a failed component, replace the ECM, monitor controller, or damaged harness sections using genuine Komatsu parts to ensure CAN protocol compatibility. After repairs, clear codes and perform a complete operational test cycle.

---

Disclaimer: This guide provides general diagnostic information. Complex electrical issues on heavy equipment should be diagnosed by qualified technicians with proper training and equipment. Always consult the official Komatsu service manual for your specific machine serial number before performing repairs.