What is Komatsu PC138US-8 Fault Code DW45KB?

Fault Code DW45KB indicates a malfunction in the diesel particulate filter (DPF) differential pressure sensor circuit on the Komatsu PC138US-8 excavator. This code is triggered when the engine control module (ECM) detects an abnormal voltage signal or open/short circuit condition in the differential pressure sensor that monitors exhaust backpressure across the DPF.

This sensor is critical for Tier 4 Final emissions compliance on the PC138US-8's SAA4D107E-3 engine. The ECM relies on accurate differential pressure readings to determine DPF soot loading levels and initiate regeneration cycles. When this circuit fails, the engine cannot properly manage emissions control, potentially leading to reduced performance and non-compliance with environmental regulations. For used excavators, this fault often signals aging electrical components or sensor degradation from prolonged exposure to exhaust heat and vibration.

Common Symptoms

• Yellow warning light illuminated on the instrument cluster with DPF-related message displayed
• Engine derate mode activated, limiting maximum engine RPM to approximately 1,800-2,000 RPM
• Inability to initiate manual DPF regeneration through the operator interface
• Intermittent loss of power during high-load operations like digging or lifting
• Excessive black smoke from exhaust stack during acceleration (in severe cases where regeneration fails)

Potential Causes

The most common technical causes for DW45KB on used PC138US-8 excavators include:

• Differential pressure sensor failure due to carbon buildup on sensor ports or internal diaphragm degradation
• Wiring harness damage at the sensor connector near the DPF canister, where heat and vibration cause wire insulation breakdown
• Corroded or loose electrical connections at the sensor plug (common on machines operating in wet or corrosive environments)
• Blocked pressure sensing tubes connecting the sensor to DPF inlet/outlet measurement points
• ECM internal fault (rare, but possible on high-hour machines with previous electrical issues)
• Aftermarket DPF replacement with incompatible sensor specifications

How to Troubleshoot and Fix Code DW45KB

Step 1: Visual Inspection Begin by inspecting the differential pressure sensor located on the right side of the engine near the DPF assembly. Check for physical damage, carbon accumulation blocking the sensing ports, and examine the wiring harness for chafing, burns, or breaks. On used excavators, pay special attention to harness routing where it passes near hot exhaust components—this is a known wear point on the PC138US-8.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals (typically 1,000-3,000 ohms at room temperature—consult the Komatsu service manual for exact specifications). Check for voltage supply at the harness side: you should see approximately 5 volts reference voltage from the ECM. Test for continuity between sensor pins and ECM connector, and check for shorts to ground.

Step 3: Pressure Tube Verification Disconnect the rubber pressure sensing tubes from both the sensor and DPF tap points. Visually inspect for blockages and blow compressed air through the tubes to clear any carbon deposits. Replace tubes if they're cracked or collapsed—a common issue on machines with 4,000+ operating hours.

Step 4: Sensor Replacement and Verification If testing reveals sensor failure, replace with a genuine Komatsu differential pressure sensor (Part # 6754-81-7410 or equivalent). After installation, clear the fault code using Komatsu KOMTRAX diagnostic software or a compatible scan tool, then perform a stationary regeneration to verify proper operation. Monitor live data to confirm the sensor provides appropriate voltage changes (0.5-4.5V range) during regeneration.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC138US-8 service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs to emissions systems may violate environmental regulations.