TL : DR = DPF Soot can be removed, DPF Ash can't. Maybe look into new, good quality, DPF. Maybe an EGR & DPF Delete with Remap.
in addition to DPF Soot content (the figure that everyone commonly knows as the 'fill percentage') they also have an Ash content value. Ash content is very hard to accurately measure and is usually a 'calculated' figure with some clever math employed by dealer level diagnostic kit (id be suprised if its intergrated into programs like MES or handheld generic scanners) that is based on number of regens/regen times/successful regen completions/exhaust gas pressure differential between upstream and downstream of the DPF etc etc.
The engine ECU clears the DPF of soot by periodically increasing the amount of fuel injected. This raises the temperature of the exhaust gasses to around 450-500*C, regens will start at anything over 200-250*C (I've personally seen active regen temps of >800*C, but it depends on which technology of Regen is employed by the manufacturer). The ECU doesnt, however, account for Ash removal.
in my experience (2 years with Mercedes commercial vehicles) it is *sometimes* possible to lower the ash content with a good run in 3rd or 4th gear at motorway speeds with a forced regen. The problem is that with each regen (passive or active) you create more ash. The larger ash particles are more difficult to get out of the DPF, which is why the higher engine speeds are needed but its a vicious cycle... regen creates ash, ash blocks a DPF, flow is restricted through the DPF and critical engine speeds cant be reached because of back pressure, which means the ECU thinks the DPF is blocked with soot, ECU activates a regen, regens create ash... rinse and repeat.
You *may* be experiencing a DPF blocked by ash rather than soot. There are companies who jetwash the ash from the DPF but i have never heard of it being 100% successful. For a similar price of a decent quality DPF, you can get them removed and have an EGR and DPF delete 'remap' on the ECU, never to worry about it ever again. ultimately its upto you but the option is there.
'07 159 Lusso Saloon, 2.4 JTDm, Oltremare Blue.
'99 Fiat Coupe, 2.0 20v VIS, Portofino Blue, Full Leather, Mani-Back Longlife Custom S/S Exhaust.