The Truth About Forced Regen

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While DPF and DEF systems are often combined together when it comes to diesel truck mechanics, they require different care and attention. A frequent mistake of semi-truck owners is to believe that a “Forced Regen” is enough to fix a DEF/DPF issue. Generally, a DEF/DPF issue will be caused by an underlying problem. This problem can lead to the malfunctioning of several engine components. Therefore, you will have to diagnose it accurately before proper action can be taken.

How DPF and DEF Work

DPF is an acronym for Diesel Particulate Filters. Their primary purpose is to trap soot particles from the flow of exhaust gases. During the regeneration stage, the DPF is heated until the collected soot is oxidized and turned into ash and carbon dioxide gas, which in turn helps manage air pollution. DPFs have become required components of diesel trucks since 2007, based on 2004 Carbon emission regulation standards. DPFs run on high temperatures to burn off particulate matter; therefore, even a minor problem can cause an array of issues ranging from power loss to bad smells. HD-OBD engine management systems monitor the aftertreatment system for soot load in the DPF and for any electronic system faults. The HD-OBD engine management system will notify the driver of problems by illuminating specific warning lamps.

DEF, which stands for Diesel Exhaust Fluid, has been a requirement for EPA 2013 International truck models and later. DEF is used to control the level of Nitrogen Oxide emissions using a chemical process known as SCR (selective catalytic reduction), DEF is a non-toxic fluid that is stored in a separate frame rail tank. DEF has a mild ammonia smell and will evaporate if left open to the atmosphere. Leaks in the DEF delivery system are easy to find because evaporated DEF leaves behind a noticeable white residue. Filling the DEF tank with a fluid other than DEF can have disastrous (and very costly) effects on your engines.

Symptoms and Causes of DPF and DEF Problems

City driving, particularly in the winter when the vehicle struggles to get up to optimal temperature, can cause accelerated DPF soot loading. Excessive soot can be caused by engine system issues. Most truck owners are likely to focus on minimizing soot levels, as poor maintenance is frequently to blame for DPF issues. However, you will also need to consider the following potential causes:

  • Over-fueling
  • EGR system malfunction
  • Leaks in the exhaust or charge air cooler systems
  • Poor servicing (the use of engine oil which does not adhere to the Low Ash and Low Sulphur standards)
  • Poor regeneration as the result of high mileage

DPF problems can make your engine lose power, have a lower fuel economy, and cause poor throttle responses, and can make your engine harder to start.

DEF system problems are generally caused by sensor and injector failures. These failures can limit engine performance and prevent the vehicle from moving.

Understanding The Consequences of Malfunctioning DEF/DPF systems

On a micro level, engine emissions system issues can produce hydrocarbons in the exhaust surpassing the prescribed level. This action accelerates the accumulation of soot in the DPF. If soot levels reach the point where exhaust cannot flow through filters easily, abnormal pressure begins to impact engine performance. This is usually the point where you will see the aftertreatment indicator lights illuminate, if illuminated warning lights are ignored, engine performance is reduced to the point of limp mode. At this point, the HD-OBD engine system will prevent you from running a stationary regeneration by activating a “lock-out”. This would require a vehicle to be towed to a service center so a forced regen could be performed with engine diagnostic software.

DEF system issues or low DEF tank levels can cause a reduction in engine performance. The HD-OBD engine system will notify the driver of these issues by illuminating specific DEF level or engine system warning lights. Ignoring these warning lamps will result in progressive engine performance reduction up to limp mode.

How Forced Regen Will Affect Your DPF and DEF

Forced regens are performed using engine diagnostic software. The software can override the “lockout”. The purpose of this action is to raise exhaust temperatures, in order to oxidize and remove the soot captured in the DPF. If the forced regen is successful, DPF errors can be cleared with diagnostic software and engine performance will be returned to normal. Frequent forced regens indicate a system issue that needs looked into. Replacing a plugged or damaged DPF without determining the cause of failure can be a costly mistake. DPF’s can be removed from the vehicle and cleaned if repair practices indicate so.

A Forced Regen is no cure for DEF/DPF system problems. Proper engine system diagnosis is required to establish the root cause of DEF/DPF issues. Replacing parts without diagnosing cause of failure is a costly and bad practice. Make sure your service center is making repairs that tackle the root of the issue. Otherwise, you could experience a high repair cost and repeated failures

Ask your local Summit parts department to learn more about forced regen, and schedule an appointment for your truck!