Whether you’re hauling cross-country or doing local runs, your emissions system is not optional—it must function flawlessly. At the heart of that system is the DEF (Diesel Exhaust Fluid) head unit. For Freightliner trucks with Cummins ISX15, ISL, or ISB 6.7 engines, the OEM 04-31677-001 DEF head ensures accurate sensing and dosing. When it fails, you may face warning codes, forced derates, or even system lockouts—none of which are ideal on the highway.
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Monitors DEF fluid level, temperature, and urea concentration, sending clean data to the ECU
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Regulates precise dosing of DEF into the exhaust so the SCR (Selective Catalytic Reduction) system can properly reduce NOx emissions
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Built to OEM 04-31677-001 tolerances for drop-in compatibility with Freightliner / Cummins setups
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Helps avoid fault codes, emission warnings, and engine derates triggered by sensor drift or incorrect readings
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Designed to withstand vibration, temperature swings, and exposure to DEF’s corrosive nature
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Straightforward replacement minimizes downtime and restores emissions integrity
Don’t wait until your engine derates or your check engine light illuminates. Installing the correct OEM 04-31677-001 Freightliner DEF Head Unit restores the integrity of your emissions feedback loop, protects your SCR system, and keeps your truck running clean, compliant, and reliable. When your operation depends on uptime, this truly is one component you can’t afford to treat as optional.