Komatsu PC240LC-10 Fault Code DW91KA: Technical Guide

What is Komatsu PC240LC-10 Fault Code DW91KA?

Fault code DW91KA indicates a malfunction in the diesel particulate filter (DPF) differential pressure sensor circuit on the Komatsu PC240LC-10 excavator. This code is triggered when the engine control module (ECM) detects abnormal voltage signals or circuit integrity issues from the differential pressure sensor that monitors exhaust backpressure across the DPF.

The differential pressure sensor plays a critical role in Tier 4 Final emissions compliance by measuring the pressure difference between the inlet and outlet of the DPF system. When this sensor fails or provides erratic readings, the ECM cannot accurately determine when regeneration cycles are needed, potentially leading to engine derate conditions and reduced machine productivity. For the PC240LC-10's Komatsu SAA6D107E-3 engine, maintaining proper DPF function is essential for both regulatory compliance and optimal fuel efficiency.

Common Symptoms

When fault code DW91KA is active, operators typically experience:

• Yellow warning light illuminated on the instrument cluster with possible DPF system alert
• Engine derate mode activated after prolonged code presence, limiting maximum RPM to approximately 1,800
• Automatic regeneration cycles failing to initiate or complete properly
• Excessive black smoke during acceleration due to incomplete combustion management
• ECM storing multiple related codes including DPF system warnings or regeneration failure codes

Potential Causes

The most common technical reasons for DW91KA on used PC240LC-10 excavators include:

• Corroded or damaged wiring harness at the sensor connector, especially where the harness routes near the exhaust system and experiences heat cycling
• Failed differential pressure sensor due to carbon buildup, internal diaphragm failure, or sensor drift from extended use
• Blocked or kinked pressure sensing tubes (rubber hoses) connecting the sensor to DPF inlet/outlet ports
• Poor electrical connections at the sensor plug or ECM connector pins caused by moisture intrusion or vibration wear
• ECM voltage supply issues providing incorrect reference voltage (typically 5V) to the sensor circuit
• Aftermarket DPF cleaning that damaged or dislodged sensing port fittings

How to Troubleshoot and Fix Code DW91KA

Step 1: Visual Inspection and Connection Check Begin by locating the differential pressure sensor mounted on the left side of the engine near the turbocharger outlet. Inspect both rubber sensing tubes for cracks, kinks, or carbon blockages—on used excavators, these tubes frequently deteriorate from heat exposure. Disconnect the electrical connector and examine pins for corrosion, bent contacts, or carbon tracking. Clean contacts with electrical contact cleaner and apply dielectric grease before reconnection.

Step 2: Electrical Circuit Testing Using a digital multimeter, backprobe the sensor connector with the ignition on (engine off). Verify the ECM provides approximately 5.0V reference voltage on the signal wire. Check for proper ground continuity (less than 0.5 ohms resistance to chassis ground). With the sensor disconnected, measure sensor internal resistance—typical values range from 2,000 to 6,000 ohms between signal and ground terminals. Values outside this range indicate sensor replacement is necessary.

Step 3: Pressure Tube and Port Verification Remove both sensing tubes from the DPF and blow compressed air (maximum 30 PSI) through each tube separately to verify they're clear. Inspect the pressure port fittings on the DPF canister for carbon buildup or physical damage. On used machines with high hours, these ports often become clogged, causing false readings. Clean ports carefully with a wire brush and ensure tubes seat properly without air leaks.

Step 4: Sensor Replacement and System Reset If testing confirms sensor failure, install a genuine Komatsu replacement sensor (part number 6261-71-7300 or equivalent). For used excavators, always replace both pressure sensing tubes simultaneously, as aged rubber can cause future intermittent faults. After installation, clear fault codes using Komatsu diagnostic software (KOMTRAX or KDW) and perform a manual regeneration cycle to verify proper system operation.

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Disclaimer: This guide provides general troubleshooting information for experienced diesel mechanics. Always consult the official Komatsu PC240LC-10 service manual and follow manufacturer safety procedures. If unfamiliar with high-voltage systems or emissions components, seek assistance from a certified Komatsu technician or authorized service center.