Driving a motorhome powered by the Cummins X12 is all about combining performance, efficiency, and emissions compliance. One of the least obvious—but absolutely critical—components making that possible is the DEF (Diesel Exhaust Fluid) Head Unit. For Tiffin Motorhomes running the X12 engine, the OEM 4310-18-39 DEF head ensures your system can accurately measure fluid properties, dose urea, and communicate with your ECU. When it fails or drifts, you face error codes, derates, or emissions faults—and none of those make for a restful road trip.
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Monitors DEF fluid level, temperature, and urea concentration, relaying precise feedback to your engine controller
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Ensures precise urea dosing into the exhaust stream so the SCR (Selective Catalytic Reduction) system can reduce NOx emissions effectively
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Manufactured to match OEM 4310-18-39 tolerances, making it a drop-in replacement with correct calibration
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Helps prevent emissions warnings, fault codes, or engine derates triggered by sensor drift or failure
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Built to endure rigors of road use—vibration, temperature swings, and the chemical stress of DEF fluid
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Offers field-friendly installation to minimize downtime on your motorhome
Many motorhome owners push off DEF head maintenance until a warning light appears. But by that time, you may already be locked into reduced power or regulatory fault codes. Installing the correct OEM 4310-18-39 Tiffin Cummins X12 DEF Head Unit restores the integrity of your emissions feedback loop, protects your SCR system, and helps ensure your journey stays smooth, clean, and worry-free. When your rig demands reliability, this is one part you can’t afford to skip.






















































































































































































































































