Komatsu PC138US-8 Fault Code DW43KB: Complete Diagnostic Guide

What is Komatsu PC138US-8 Fault Code DW43KB?

Fault code DW43KB on the Komatsu PC138US-8 indicates a communication error between the engine controller (ECM) and the machine controller (MCU), specifically related to CAN bus data transmission failure. This code triggers when the Engine Control Module fails to receive or transmit critical operational data to the Machine Control Unit within the expected timeframe.

This communication link is essential for coordinating engine performance with hydraulic demand, monitoring emission controls, and ensuring proper derate strategies. On the PC138US-8 model equipped with the SAA4D107E-2 engine, this fault directly impacts fuel efficiency, throttle response, and the machine's ability to adjust power output based on hydraulic load requirements.

Common Symptoms

When DW43KB is active, operators typically experience:

• Engine warning lamp illuminated on the monitor panel, often accompanied by a fault code display
• Reduced engine power or sudden derate to idle speed, preventing normal operation
• Erratic throttle response where engine RPM doesn't match dial settings
• Intermittent loss of monitor display functions, including fuel level, coolant temperature, or hour meter readings
• Hydraulic system sluggishness due to improper engine-pump coordination

Potential Causes

The most common technical causes for DW43KB on used PC138US-8 excavators include:

• CAN bus wiring harness damage at known rub points near the engine mount bracket and along the right-side frame rail where vibration causes insulation wear
• Corroded or loose connectors at the ECM (located under the operator's cab) or MCU (mounted behind the monitor panel)
• Failed termination resistors on the CAN network, typically 120-ohm resistors that deteriorate over time
• ECM or MCU internal failure, more common in machines exceeding 8,000 operating hours
• Voltage supply issues to either controller, often caused by failing alternator or poor ground connections at the battery tray

How to Troubleshoot and Fix Code DW43KB

Step 1: Visual Inspection Begin by inspecting the CAN bus harness running between the engine bay and operator's cab. On used excavators, check for wire chafing at the engine mount area and where the harness passes through the bulkhead. Look for green corrosion on connector pins at both the ECM (6-pin CAN connector) and MCU terminals.

Step 2: Electrical Testing Using a digital multimeter, measure CAN-High and CAN-Low resistance between the ECM and MCU. You should read approximately 60 ohms with both controllers connected (indicating proper 120-ohm termination at each end). Disconnect both controllers and measure each termination resistor individually—each should read 120 ohms ±5%.

Step 3: Voltage and Signal Verification With the key switch ON (engine off), verify battery voltage (12-14V) at ECM pin B+ and MCU power supply. Using Komatsu KOMTRAX diagnostic software or an aftermarket J1939 scanner, monitor live CAN bus traffic. If no communication appears, suspect wiring breaks or controller failure.

Step 4: Component Replacement Strategy For used machinery, never replace controllers first. Replace damaged harness sections using shielded twisted-pair CAN cable (avoid standard wire). Clean all connector pins with electrical contact cleaner and apply dielectric grease. If testing confirms controller failure, verify software version compatibility—mismatched ECM/MCU firmware versions can cause persistent communication faults.

---

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic services for complex electrical issues. Improper troubleshooting can cause additional damage to electronic components.