Komatsu PC138USLC-8 Fault Code DW45KB: Complete Diagnostic Guide

What is Komatsu PC138USLC-8 Fault Code DW45KB?

Fault Code DW45KB indicates a communication error or data link failure between the excavator's Engine Control Module (ECM) and the Machine Controller, specifically related to CAN (Controller Area Network) bus communication issues on Komatsu's Dash-8 series machines.

This code appears when the machine controller cannot properly receive or transmit signals from the engine ECM through the primary data network. On the PC138USLC-8, this communication failure disrupts critical functions including engine performance monitoring, hydraulic system coordination, and operational diagnostics. The CAN bus serves as the central nervous system for modern excavators, making this fault particularly serious for overall machine performance and safety.

Common Symptoms

When DW45KB is active, operators typically experience:

• Intermittent or complete engine derate, limiting RPM to 1500 or lower regardless of throttle position
• Multiple warning lights illuminating simultaneously on the monitor panel, including engine and hydraulic system alerts
• Loss of monitor display functions, with the screen showing error messages or going blank
• Erratic hydraulic response, particularly during combined functions like boom and swing operations
• Inability to access diagnostic information through the standard machine monitor

Potential Causes

The most common technical reasons for DW45KB on used PC138USLC-8 excavators include:

• Corroded or damaged CAN bus connectors at the ECM (located under the right side cover) or machine controller harness connections
• Chafed or broken wiring in the harness routing near the engine mount points where vibration causes wear over time
• Faulty termination resistor on the CAN network (120-ohm resistor failure is common on older Dash-8 models)
• ECM or machine controller internal failure, particularly on machines exceeding 6,000 operating hours
• Low voltage conditions from weak batteries or poor ground connections affecting controller stability
• Aftermarket component interference, especially non-OEM monitors or improperly installed accessories

How to Troubleshoot and Fix Code DW45KB

Step 1: Perform Visual Inspection Begin by inspecting all wiring harnesses between the engine compartment and cab. On used excavators, check specifically where harnesses pass through the swing bearing area and near the engine mounts—these are known friction points. Look for chafing, cuts, or exposed copper wire. Inspect all connector pins for corrosion, bent terminals, or moisture intrusion.

Step 2: Check CAN Bus Integrity Using a digital multimeter, measure resistance across the CAN-High and CAN-Low terminals at the ECM connector (typically pins 23 and 24 on the PC138USLC-8). With the key off and both controllers connected, you should read approximately 60 ohms (two 120-ohm termination resistors in parallel). A reading significantly higher indicates an open circuit or failed termination resistor.

Step 3: Verify Power and Ground Check battery voltage—should be 12.5V minimum with key off, 13.8-14.4V running. Inspect the main ground strap from battery to frame and the ECM ground connection. Poor grounds are extremely common on used machines and cause intermittent communication failures.

Step 4: Test with Diagnostic Software Connect Komatsu KOMTRAX or compatible diagnostic software to isolate whether the ECM or machine controller is the non-communicating component. Monitor live CAN bus traffic to identify if messages are being sent but not received, or not sent at all.

Step 5: Inspect Termination Resistors Locate the CAN termination resistors (one at the ECM, one at the machine controller). These can fail open on older machines. Test each resistor independently—should measure 120 ohms ±5%.

For used excavators, always clean and apply dielectric grease to all CAN bus connectors before replacing expensive controllers. Approximately 70% of DW45KB codes on used equipment resolve through harness repair and connector maintenance rather than component replacement.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific serial number range and consider professional diagnostic assistance for complex electrical issues. Improper repairs to CAN bus systems can cause additional controller damage.