What is Komatsu PC240LC-8M0 Fault Code DR21KX?

Fault Code DR21KX indicates a malfunction in the diesel particulate filter (DPF) differential pressure sensor circuit or an abnormal pressure reading within the exhaust aftertreatment system. This code specifically relates to the exhaust gas monitoring system on the Komatsu SAA6D107E-1 engine, which powers the PC240LC-8M0 model. The differential pressure sensor measures the pressure difference before and after the DPF to determine filter loading and trigger regeneration cycles when necessary.

This fault is critical because the engine control module (ECM) relies on accurate DPF pressure data to manage exhaust system health and prevent catalytic converter damage. If left unaddressed, the code can trigger engine derate modes, reducing power output to protect emission control components. For used excavators, this sensor circuit is particularly vulnerable to age-related failures, including harness degradation and connector corrosion from constant exposure to exhaust heat and environmental contaminants.

Common Symptoms

• Amber or red warning light illuminated on the instrument cluster, often accompanied by a DPF regeneration indicator
• Reduced engine power (derate mode) limiting hydraulic system performance and travel speed
• Frequent or unsuccessful automatic regeneration attempts, causing the machine to enter standby mode repeatedly
• Black smoke from the exhaust during operation, indicating incomplete combustion or DPF overload
• Error messages displayed on the monitor panel specifically referencing exhaust system faults

Potential Causes

The most common technical reasons for DR21KX on used PC240LC-8M0 excavators include:

• Faulty differential pressure sensor due to carbon buildup on sensor ports or internal sensor element failure
• Damaged or corroded wiring harness near the DPF housing where heat and vibration cause insulation breakdown
• Clogged DPF pressure sensing tubes blocked by soot, ash, or moisture accumulation
• Poor electrical connections at the sensor connector, particularly corrosion on pin terminals from exhaust condensation
• ECM communication errors or software calibration issues affecting sensor signal interpretation
• Physical DPF damage causing abnormal exhaust backpressure that exceeds sensor parameters

How to Troubleshoot and Fix Code DR21KX

Step 1: Connect Diagnostic Software Use Komatsu KOMTRAX or compatible diagnostic software to retrieve active and stored codes. Record freeze frame data showing sensor voltage readings and pressure values. Normal differential pressure sensor voltage ranges between 0.5-4.5V depending on filter load.

Step 2: Inspect Physical Components Visually examine the DPF differential pressure sensor mounted on the exhaust assembly. Check sensing tubes for blockages—carbon deposits frequently obstruct these small-diameter hoses on used machines. Inspect the wiring harness for heat damage, abrasion against frame members, and connector seal integrity.

Step 3: Perform Electrical Tests Disconnect the sensor and use a digital multimeter to check sensor resistance (typically 200-800 ohms) and voltage supply from the ECM (should read 5V reference). Test harness continuity from sensor connector to ECM pins, specifically checking for shorts to ground or open circuits.

Step 4: Clean or Replace Components For used excavators, clean the DPF pressure sensor ports using compressed air and appropriate solvents before replacement. If electrical values are out of specification, replace the sensor (Komatsu part number 6754-21-7110). Replace any compromised harness sections with heat-resistant wiring and apply dielectric grease to connectors.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual and consider professional diagnostic assistance for complex repairs.