Cummins DEF Head Unit : OEM ASP-908-2321-297

Reliable DEF Delivery Control for Cummins SCR Systems

What is it?
The Cummins DEF Head Unit, referenced by OEM part number ASP-908-2321-297, is a core component of the Diesel Exhaust Fluid (DEF) dosing system used in Cummins-equipped diesel engines. This module works with onboard sensors and the engine control unit (ECU) to accurately meter DEF into the exhaust stream, helping support nitrogen oxide (NOx) reduction through the Selective Catalytic Reduction (SCR) process.

Why choose this DEF Head Unit?
Manufactured to meet Cummins’ original specifications, this DEF head unit is designed for a direct replacement and seamless interaction with the vehicle’s aftertreatment system. When the dosing head becomes worn, clogged, or otherwise compromised, it can deliver incorrect amounts of DEF, which may trigger emissions warnings, uneven SCR response, or compliance issues. Installing the correct OEM-specified head unit helps maintain reliable DEF delivery and coordinated emissions system operation.

Key Benefits
✅ Engineered to Cummins original standards for DEF dosing systems
✅ Ensures accurate DEF metering for NOx conversion
✅ Promotes coordinated emissions control with sensors and the ECU
✅ Direct replacement — no fabrication or modifications required
✅ Built to withstand heavy-duty exhaust environments

Applications
This DEF head unit is compatible with a range of Cummins-equipped medium- and heavy-duty vehicles and equipment that use SCR aftertreatment systems requiring precision DEF dosing. Typical applications include long-haul tractors, vocational trucks, regional fleets, and other commercial diesel platforms where regulated emissions performance is essential.

Installation Notes
Before servicing, allow the aftertreatment system to cool fully to avoid injury or component damage. Disable the ignition and disconnect the battery. Carefully disconnect DEF supply and return lines, electrical connectors, and mounting hardware from the existing head unit. Inspect lines, seals, and harnesses for wear or contamination before installing the new unit. Position the replacement DEF head unit, secure it with proper fasteners, and reconnect all fluid lines and electrical connectors. After installation, clear any stored fault codes and verify accurate DEF dosing with appropriate diagnostics.

Final Thoughts
If your Cummins-equipped vehicle is experiencing DEF-related fault codes, inconsistent NOx readings, or uneven aftertreatment behavior, replacing the DEF head unit with the correct OEM-specified part can help restore dependable fluid control and coordinated SCR performance. The Cummins DEF Head Unit (OEM ASP-908-2321-297) plays a central role in regulated exhaust treatment and helps support reliable engine operation across varied duty cycles.