What is Komatsu PC200-10 Fault Code DAFGMC?

Fault Code DAFGMC on the Komatsu PC200-10 excavator indicates a "DEF (Diesel Exhaust Fluid) After-treatment Fuel Gas Mixture Control" malfunction within the emissions control system. This code specifically points to issues with the doser injector circuit or the DEF delivery system that controls the precise mixture of diesel exhaust fluid being injected into the exhaust stream for SCR (Selective Catalytic Reduction) operation.

This fault is critical because the PC200-10's Tier 4 Final or EU Stage IV compliant engine relies on proper DEF dosing to reduce NOx emissions. When the system cannot accurately control the fuel gas mixture in the aftertreatment process, the excavator's ECM (Engine Control Module) may trigger power derate to prevent emissions violations and potential DPF (Diesel Particulate Filter) or SCR catalyst damage.

Common Symptoms

• Amber or red warning light on the instrument cluster, specifically the DEF system indicator
• Engine power derate (typically 25-40% reduction) after a predetermined time period if the fault remains unresolved
• DEF consumption irregularities—either excessive usage or no consumption at all
• Frequent DPF regeneration cycles due to improper exhaust treatment
• Error message on monitor display indicating aftertreatment system malfunction

Potential Causes

The DAFGMC code on used PC200-10 excavators typically stems from specific wear-related issues:

• DEF doser injector failure or clogged nozzle due to crystallized urea deposits (common in machines with 3,000+ hours)
• Wiring harness damage at the doser connector—known rub point near the exhaust mounting bracket on this model
• ECM communication errors with the doser control module due to corroded pins in the 12-pin aftertreatment harness connector
• DEF quality issues causing sensor contamination or injector clogging (contaminated or expired DEF)
• DEF pump failure preventing adequate pressure (normally 87-116 psi) to the doser
• Faulty pressure or temperature sensors in the DEF tank or supply line

How to Troubleshoot and Fix Code DAFGMC

Step 1: Connect Diagnostic Software Use Komatsu KOMTRAX or compatible diagnostic software to read live data. Check DEF pressure readings (should be 87-116 psi during operation), DEF temperature, and doser command vs. actual delivery rates. Note any secondary codes related to the aftertreatment system.

Step 2: Inspect DEF Doser and Wiring Physically inspect the DEF doser injector mounted on the decomposition tube. Check for white crystalline buildup indicating urea deposits. On used excavators, carefully examine the wiring harness where it passes near the turbocharger and exhaust components—heat and vibration create known failure points. Use a multimeter to check doser resistance (typically 3-6 ohms) and verify supply voltage (12V when commanded).

Step 3: Test DEF System Pressure and Quality Check DEF tank quality using a refractometer (proper concentration is 32.5% urea). Verify DEF pump operation and pressure using a mechanical gauge at the test port. Inspect all DEF line connections for corrosion, especially the quick-disconnect fittings prone to galvanic corrosion in older machines.

Step 4: Clean or Replace Components For used excavators, attempt doser cleaning with approved DEF system cleaner before replacement. Replace the doser injector if resistance is out of spec or flow testing fails. Clean all harness connectors with electrical contact cleaner and apply dielectric grease. Replace any corroded wiring sections rather than the entire harness when possible.

Step 5: Clear Codes and Verify Repair After repairs, perform a forced regeneration if possible, clear all fault codes, and operate the machine under load while monitoring DEF consumption and pressure with diagnostic software.

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Disclaimer: This guide provides general troubleshooting information for the Komatsu PC200-10 DAFGMC fault code. Emissions system repairs require proper training and equipment. Always consult the official Komatsu service manual and consider professional diagnostic assistance for complex aftertreatment issues. Improper repairs may result in emissions non-compliance or catalytic system damage.