In medium-duty trucks and buses powered by the Cummins ISB 6.7L engine, the DEF (Diesel Exhaust Fluid) system plays a vital role in controlling NOx emissions via the SCR (Selective Catalytic Reduction) process. The DEF head unit—specifically built to OEM 2515900C1 specifications—serves as the brain of that system, monitoring fluid level, concentration, and temperature, and ensuring accurate dosing. When this head unit is faulty or out of spec, your vehicle can trigger warning codes, suffer reduced emissions efficiency, or even face derates that impact uptime.
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Continuously monitors DEF fluid level, temperature, and urea concentration, providing crucial data to the engine’s ECU
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Controls the dosing of DEF into the exhaust system so the SCR catalyst receives the correct amount of urea for NOx reduction
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Designed to OEM 2515900C1 tolerances to ensure proper fit, calibration, and system compatibility for Navistar/International ISB 6.7L applications
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Helps prevent common issues such as DEF system error codes, inaccurate fluid level readings, or emissions control derates
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Built to endure the demanding conditions of heavy-duty duty cycles—vibration, temperature swings, and exposure to DEF chemistry
Installing the correct DEF head unit is more than just a replacement—it’s restoring the accuracy and reliability of your entire emissions feedback loop. With this OEM-matched unit in place, your Navistar/International ISB 6.7L vehicle stands a far better chance of staying compliant, reliable, and ready for the job.




















































































































































































































































































