A method to determine the actual quantity (ṁ ASH) of metal powders or ashes trapped in a particulate filter for an internal combustion engine of a vehicle comprising the steps of: estimating a first value of the quantity (ṁ ASH_EST) of metal powders trapped in the particulate filter based on a first model (20, 21, 22, 23) using measured and/or given physical quantities; measuring a second value of the quantity (ṁ ASH _ M) of metal powders trapped in the particulate filter based on a second model, which uses the pressure drop (ΔP) at the ends of the particulate filter for which the quantity (ṁ ASH _ M) of metal powders trapped in the particulate filter is responsible, and the volume flow rate (ṁ EXH) of the exhaust gases produced by the internal combustion engine and flowing into the particulate filter; said measuring step comprises the sub-steps of: - detecting the pressure drop (ΔP) at the ends of the particulate filter through a differential pressure sensors at the ends of the particulate filter; - determining a quantity (ṁ GPF) of particulate trapped in the particulate filter; - determining the pressure drop at the ends of the particulate filter for which the quantity (ṁ GPF) of particulate trapped in the particulate filter is responsible; and - calculating the pressure drop at the ends of the particulate filter for which the quantity (ṁ ASH _ M) of metal powders trapped in the particulate filter is responsible through the difference between the pressure drop at the ends of the particulate filter and the pressure drop at the ends of the particulate filter for which the quantity (ṁ GPF) of particulate trapped in the particulate filter is responsible; updating the first value as a function of the second value of the quantity (ṁ ASH _ M) of metal powders trapped in the particulate filter; and determining the actual quantity (ṁ ASH) of metal powders or ashes trapped in the particulate filter as a function of the update of the first value. estimating a first value of the quantity (ṁ ASH_EST) of metal powders trapped in the particulate filter based on a first model (20, 21, 22, 23) using measured and/or given physical quantities; measuring a second value of the quantity (ṁ ASH _ M) of metal powders trapped in the particulate filter based on a second model, which uses the pressure drop (ΔP) at the ends of the particulate filter for which the quantity (ṁ ASH _ M) of metal powders trapped in the particulate filter is responsible, and the volume flow rate (ṁ EXH) of the exhaust gases produced by the internal combustion engine and flowing into the particulate filter; said measuring step comprises the sub-steps of: - detecting the pressure drop (ΔP) at the ends of the particulate filter through a differential pressure sensors at the ends of the particulate filter; - determining a quantity (ṁ GPF) of particulate trapped in the particulate filter; - determining the pressure drop at the ends of the particulate filter for which the quantity (ṁ GPF) of particulate trapped in the particulate filter is responsible; and - calculating the pressure drop at the ends of the particulate filter for which the quantity (ṁ ASH _ M) of metal powders trapped in the particulate filter is responsible through the difference between the pressure drop at the ends of the particulate filter and the pressure drop at the ends of the particulate filter for which the quantity (ṁ GPF) of particulate trapped in the particulate filter is responsible; - detecting the pressure drop (ΔP) at the ends of the particulate filter through a differential pressure sensors at the ends of the particulate filter; - determining a quantity (ṁ GPF) of particulate trapped in the particulate filter; - determining the pressure drop at the ends of the particulate filter for which the quantity (ṁ GPF) of particulate trapped in the particulate filter is responsible; and - calculating the pressure drop at the ends of the particulate filter for which the quantity (ṁ ASH _ M) of metal powders trapped in the particulate filter is responsible through the difference between the pressure drop at the ends of the particulate filter and the pressure drop at the ends of the particulate filter for which the quantity (ṁ GPF) of particulate trapped in the particulate filter is responsible; updating the first value as a function of the second value of the quantity (ṁ ASH _ M) of metal powders trapped in the particulate filter; and determining the actual quantity (ṁ ASH) of metal powders or ashes trapped in the particulate filter as a function of the update of the first value.