Diesel Particulate Filters (DPF) are a key component in many on- and off-road aftertreatment systems to meet increasingly stringent particle emissions limits. Efficient thermal management and regeneration control is critical for reliable and cost-effective operation of the combined engine and aftertreatment system. Conventional DPF control systems predominantly rely on a combination of filter pressure drop measurements and predictive models to indirectly estimate the soot loading state of the filter. Over time, the build-up of incombustible ash, primarily derived from metal-containing lubricant additives, accumulates in the filter to levels far exceeding the DPF's soot storage limit. The combined effects of soot and ash build-up dynamically impact the filter's pressure drop response, service life, and fuel consumption, and must be accurately accounted for in order to optimize engine and aftertreatment system performance.This work applied a radio frequency (RF) sensor to directly monitor diesel particulate filter soot and ash levels, thereby enabling direct feedback control of the filter based on its actual loading state. Results from fleet tests with Volvo/Mack trucks, over predominantly urban drive cycles, indicated the potential to decrease regeneration duration and associated fuel consumption by 50% to 75%, depending on operating conditions, and also to extend the time between active filter regenerations. Additional testing evaluated the performance of the sensor to distinguish soot from ash and define the DPF ash cleaning based on the actual measured ash load, as opposed to a prescribed filter maintenance interval. The results are useful to develop advanced control strategies to minimize the DPF-related fuel penalty, extend the service life of the filter, and identify anomalies indicative of filter failures or engine malfunctions.