Diesel Particulate Filter Light
Just as a gasoline engines, diesel engines release pollutants into the air we breathe. These pollutants are chemicals and compounds, that if not for our vehicles, would not end up in the air in the quantity and concentration our vehicles cause them to be. In diesel vehicles from 2007 and later a filter has been fitted into the exhaust pipe to reduce the amount of these pollutants in our air. This filter is called a Diesel Particulate Filter (PDF). It is a composite of cordierite, silicon carbide or metal fibers that traps the particulates (soot) that flow out of the exhaust pipe.
Once the PDF captures so much soot that it fills up, it actually regenerates, or cleans itself. This occurs through one of two methods: active or passive. The indicator light will be green while the DPF is regenerating. An amber light means the PDF needs to be regenerated, which happens automatically while driving. In some cases, regeneration can be done manually. If the PDF indicator light is red, that means it needs to regenerate immediately. If the filter issue is not corrected soon, the check engine light will come on and you may experience a reduction in engine power.
Active regeneration of the DPF is used when exhaust temperatures are too irregular for a passive system to regenerate consistently. Because they have very different duty cycles, many light-duty diesel trucks have active DPF systems. In fact, Ford, GM, and Dodge have all brought vehicles to market with active DPF systems. For active regeneration to occur parameters in the engine must be changed to increase the exhaust temperatures in the DPF. This requires access to the engine control unit, along with a very precise knowledge of the parameters of the engine.
Active PDF regeneration strategies include late or post-injection of fuel into the combustion chamber, changes to the turbo boost, changes to the EGR valve, intake air throttling, and retarding the injection timing. While each of these methods can indeed raise the exhaust temperature, they can also have a negative impact on the vehicle's fuel economy, power, and engine wear.
If the PDF symbol is red, it indicates that the system needs to be regenerated immediately, and engine power will be reduced if it is not. A red DPF symbol is often accompanied by a Check Engine light.