Sep 20, 2019
A common misconception in the semi truck industry is that a DEF/DPF issue can be corrected by simply performing a "Forced Regen". While in some cases excessive idle time and poor maintenance can cause soot levels to accumulate faster than usual, there is usually an underlying cause of the backed up DEF/DPF system. Issues like:
These issues create an above normal level of hydrocarbons and debris that back up the DEF/DPF filtration system faster than the standard level. This creates an environment that can't be kept up with by the basic operation of the system. Once soot levels reach the point that the exhaust is having difficulty passing through the filters the system recognizes the abnormal pressure and triggers the indicator lights on the dash and impacts the engine's performance. Often the engine goes into a derate or "limp mode" that limits the speed of the truck to 45-60 miles per hour, and eventually will shut down the engine. In most cases the DEF/DPF system will "lock out" the ability to run a stationary regeneration, thus causing the owner to head into a service center to handle the issue. This is where the common misconception arises.
It's common practice to use a laptop and make the engine to go into a "forced regen" to override the "lock out" and push the excess soot and debris out of the system. While this will often clear the "check engine" and "DPF/DEF" codes, this is only a temporary solution, as the underlying cause of the engine issue has not been corrected. In some cases repair shops will go as far as having the DEF/DPF filter cleaned or replaced without repairing the issue or issues causing the excess soot/debris problem. When the issues that caused the problem have not been addressed, the DEF/DPF system will back up and the problem will return in a very short time.
In short, beware of the "Forced Regen Cure", or DEF/DPF system repairs that stand alone in a shop's diagnosis. Question the cause of the excess soot/debris in your filtration system, try and get the repairs that you need handled the first time to avoid a recurrent DEF/DPF issue, it could save you a ton of money in the long run! If you’re experiencing these or other issues see our list of complete semi truck service here.