Soot Generation Causes And Effects

WARNING: This page is about a different car, the 2011 RAM Pickup. However, it is still accessible from the selected car via links, so may be relevant.

When trying to understand the functionality of the exhaust and aftertreatment system, (more precisely the effects on the Diesel Particulate Filter (DPF)) you must think in terms of standard plumbing principals. Everything flows downstream. Systems and components along the path are affected by the soot in the exhaust, and these components can also contribute to the soot levels (cause and effect).

This overview will attempt to elaborate on the causes and effects of the Soot flowing downstream in the system. The soot originates in the combustion chamber as a by-product of the combustion process. This is the beginning of the stream. All soot generated in the combustion chamber flows downstream. Excessive amounts of soot can be caused by faulty inputs to the engine controller, air handling system leaks or restrictions, fuel contamination, or fuel injectors. Some soot will always be generated. Under proper operating conditions, soot levels will be low and very manageable.

The next component downstream is the EGR. The EGR can be affected by soot coming from the combustion process. The soot can cause the EGR to stick open or closed, or become restricted. If the EGR malfunctions, it can cause soot generation which is then added to system.

The next component downstream is the Turbocharger. The Turbocharger can be affected by soot coming from the combustion process and/or the EGR. If the Turbocharger malfunctions (sticks, or leaks oil or coolant internally), it can cause soot generation which is then added to system.

The next components found downstream are the O2 Sensors. The O2 Sensors can be affected by soot coming from the combustion process, the EGR, and/or the Turbocharger. If an O2 Sensor malfunctions, it can cause (to a much lesser extent) soot generation which is added to system. O2 Sensor codes can be caused by excessive soot.

ALL of the soot generated upstream will land in the DPF. If a vehicle sets a DPF DTC, such as P1451 or P242F, which are related to the calculated amount of soot currently caught in the DPF this means the engine controller has calculated that the DPF is getting full. This number is and estimation, hence the name; "Estimated Soot Load Based on Delta" (ESL/D) and is measured in grams. Sometimes soot levels will be estimated high and set faults and there is little soot in the DPF!

When a DPF fault sets, it is important to root cause the reason the soot landed in the filter and could not be removed through a normal regeneration. Is fuel contamination the issue causing injectors to stick and over fuel? Is the EGR or Turbocharger sticking causing excess soot? Or is it a combination of these?

A DPF should NEVER be replaced without first determining if there is another root cause of the source of the high "Estimated Soot Load Based on Delta" and repairing this issue also. A DPF should also not be replaced without performing the AFTERTREATMENT INSPECTION GUIDELINE procedure. This will visually show you with examples how to determine if replacement of an aftertreatment component is necessary.