The DEF Module and Engine Control Module (ECM) are in direct communication to make sure the system is operational.ĮCM – The DPF system and the regeneration process is controlled by the ECM on a Cummins truck. NOx Sensors, both inlet and outlet sensors – When the sensor detects much NOx in the exhaust stream, it tells the SCR/DEF system to inject more urea, which uses ammonia to reduce emissions levels in your system.ĭEF Control Module – This module controls the operation of the emission system. If this fails, you will go into a derate immediately If you have bad DEF fluid, this can cause DEF quality issues and can put you into a derate.ĭEF Doser Valve – Regulates the injection of the DEF fluid into your SCR Catalyst.ĭEF Pump Assembly – This is the heart of your DEF system that pumps the DEF fluid throughout the DEF system. This has a level sensor and a quality sensor to make sure the concentrations are in allowable limits.

What components make up the emission system that controls the 5 MPH derate?ĭEF Fluid – The tank with the blue cap holds DEF Fluid. However, when it’s a specific 5 MPH derate then you can be certain that the problem is related to the emissions, aka the aftertreatment system. A derate can be caused by various sensors or systems. A derate is designed to protect you from causing engine or DPF damage. What is a DEF derate or an aftertreatment derate?Ī derate means that the program inside the engine computer limits either the power or vehicle speed.

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