OEM Decomposition Reactor / Mixer Module

The decomposition reactor or mixer module is where the diesel exhaust fluid (DEF) is injected into the system. This module usually has baffles in order to help distribute the DEF evenly into the exhaust stream. The decomposition reactor is typically after the DPF and before the SCR, though some vehicles do have unique configurations.

If you are replacing the mixer, you will also want to replace the gaskets on the inlet and outlet sides, and in some vehicles, you will need to replace the gasket that goes between the DEF injector and mixer as well.