Komatsu PC750SE-7 Fault Code DW91KA: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code DW91KA?

Fault Code DW91KA indicates a communication error or data link failure between the engine controller (ECM) and the machine's main monitor system on the Komatsu PC750SE-7 excavator. This code specifically relates to the CAN bus communication network that allows critical systems to exchange operational data in real-time.

This fault affects the KOMTRAX monitoring system and the machine's ability to display accurate engine parameters, hydraulic temperatures, and diagnostic information. The PC750SE-7 relies on continuous data exchange between its SAA6D140E-7 engine ECM and the machine controller to optimize performance and fuel efficiency. When this communication breaks down, operators lose visibility into critical machine health metrics, potentially leading to undetected issues that could cause expensive damage.

Common Symptoms

When DW91KA is active, operators typically experience:

• Monitor display errors or complete loss of engine parameter readings (RPM, coolant temperature, fuel level)
• Warning lights illuminated on the dashboard, particularly the master warning lamp
• Intermittent gauge fluctuations where readings drop to zero then return
• KOMTRAX data logging failures, preventing remote monitoring capabilities
• Machine may continue operating normally, but without diagnostic feedback to the operator

Potential Causes

The most common technical causes for DW91KA on used PC750SE-7 excavators include:

• CAN bus wiring harness damage from rubbing against the engine block or frame rails near the turbocharger area (known wear point on this model)
• Corroded or loose connector pins at the ECM or main monitor harness connections, especially the 38-pin ECM connector
• Failed termination resistors in the CAN network (120-ohm resistors at network endpoints)
• ECM or monitor controller internal failure, though less common than wiring issues
• Voltage supply problems to either controller due to failing alternator or battery issues
• Water intrusion into harness connectors from damaged cab floor seals

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. Look for chafed insulation, particularly where harnesses pass through bulkheads or near hot engine components. Check all connector pins for corrosion, bent terminals, or moisture. On used excavators, pay special attention to harness routing—previous repairs may have created new rub points.

Step 2: Electrical Testing Using a digital multimeter, verify battery voltage (should be 24-28V with engine running). Check CAN-High and CAN-Low wire continuity between ECM and monitor using Komatsu's wiring diagrams. Measure termination resistance across CAN-High and CAN-Low with both controllers disconnected—you should read approximately 60 ohms (two 120-ohm resistors in parallel). Any reading significantly different indicates open circuits or failed resistors.

Step 3: Advanced Diagnostics Connect Komatsu KDPF diagnostic software to read detailed communication logs and identify which controller is failing to respond. Monitor live CAN bus traffic to detect intermittent dropouts. If wiring tests pass, suspect ECM or monitor controller failure. Before replacing expensive controllers on used machines, try cleaning all connector contacts with electrical contact cleaner and applying dielectric grease—corrosion is often the culprit.

Disclaimer: This guide provides general troubleshooting information. Always consult Komatsu service manuals and qualified technicians for complex electrical diagnostics. Improper repairs may cause additional damage or safety hazards.