What is Komatsu PC210-10 Fault Code DW91KA?

Fault Code DW91KA indicates a malfunction in the DEF (Diesel Exhaust Fluid) pump system, specifically related to abnormal current or voltage detected in the DEF supply unit circuit. This diagnostic trouble code (DTC) is triggered when the machine's Engine Control Module (ECM) detects irregular electrical signals from the DEF pump motor or its associated wiring harness during operation.

The Komatsu PC210-10 utilizes a Selective Catalytic Reduction (SCR) system to meet Tier 4 Final emissions standards. The DEF pump is critical for injecting the correct amount of diesel exhaust fluid into the exhaust stream to reduce NOx emissions. When DW91KA appears, the SCR system's ability to function properly is compromised, potentially leading to engine derate or shutdown to protect emissions compliance and engine components.

Common Symptoms

When fault code DW91KA is active on your PC210-10, operators typically experience:

• Amber or red warning lamp illuminated on the instrument cluster, specifically related to the exhaust aftertreatment system
• Engine power derate occurring after a grace period (typically 4-8 hours), reducing machine performance by 25-40%
• DEF consumption abnormalities – either no DEF usage or excessive consumption patterns
• Warning messages on the monitor display indicating "SCR System Malfunction" or "Service Required"
• Potential engine shutdown if the code remains unresolved beyond the manufacturer's programmed timer

Potential Causes

The DW91KA code on used PC210-10 excavators commonly stems from:

• DEF pump motor failure due to crystallized urea buildup from contaminated or old DEF fluid
• Damaged wiring harness or corroded connectors between the ECM and DEF pump, especially at flex points near the pump mounting location
• Short circuits or open circuits in the DEF pump supply voltage lines (typically 12V circuit)
• Failed DEF pump relay or blown fuse in the supply circuit
• ECM software glitches requiring reprogramming or calibration updates
• Contaminated DEF tank causing pump internal damage from particles or frozen fluid

How to Troubleshoot and Fix Code DW91KA

Step 1: Initial Inspection and Code Verification Connect a Komatsu diagnostic tool (KOMTRAX Plus or compatible scan tool) to read active and stored codes. Document freeze frame data showing when the fault occurred. Inspect the DEF tank level – ensure adequate fluid (minimum 25%) and check expiration date on DEF containers.

Step 2: Electrical Circuit Testing Locate the DEF pump (mounted on the left side of the fuel tank assembly). Disconnect the pump electrical connector and inspect for corrosion, bent pins, or moisture intrusion. Using a digital multimeter, check supply voltage at the pump connector with ignition on – should read approximately 12-14 volts. Check ground circuit continuity (should be less than 1 ohm resistance).

Step 3: DEF Pump Resistance Check With the pump connector still disconnected, measure resistance across the pump motor terminals. Typical specifications are 3-6 ohms (consult service manual for exact values). Readings significantly outside this range indicate pump motor failure requiring DEF pump assembly replacement (Komatsu part number 6754-79-4910 or equivalent).

Step 4: Wiring Harness Inspection Trace the harness from the DEF pump to the main engine harness junction. On used excavators, pay special attention to harness routing near moving components or heat sources. Look for chafed insulation, wire rub-through points, or damaged protective loom – common failure points on machines with 3,000+ operating hours.

Step 5: DEF Quality and System Flush If electrical components test normal, drain and inspect DEF fluid quality. Contaminated or crystallized DEF requires complete system flushing including lines, pump, and injector. Refill with fresh ISO 22241-compliant DEF (API-certified).

Step 6: Component Replacement and Verification Replace faulty components (DEF pump, damaged harness sections, or corroded connectors). Clear fault codes using diagnostic software and perform a forced DEF pump prime cycle. Monitor system operation for at least 30 minutes under load to confirm repair.

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Disclaimer: This guide provides general troubleshooting information for the Komatsu PC210-10 fault code DW91KA. Always consult the official Komatsu service manual for your specific machine serial number and software version. If unfamiliar with high-pressure fuel systems or electrical diagnostics, contact a certified Komatsu technician or authorized service center to prevent injury or further equipment damage.