High DPF Residual Ash Level
Here we have an Audi Q3 2.0 TDI (2013 – 273,854 miles) booked in for a live data engine diagnostic and engine carbon clean, after the owner noticed grey smoke and sluggish performance. Both turned out to be linked to a high DPF residual ash level.
The owner has had issues for a while with declining performance, spluttering and frequent visible grey smoke. Various garages had plugged in and said nothing was amiss, so she gave us a call to diagnose and clean it up.
Initial diagnostics showed no codes, but the live data told a different story. Much of the data was good, but the injector fuelling wasn’t ideal; not unexpected given the mileage.
The main issue seems to be the DPF. Soot levels very low, but pressures high and DPF residual ash level way over the limit. This scenario would lead to grey smoke (ash literally spilling out of the exhaust) and almost continual regeneration.
What Is DPF Residual Ash and Why Does It Matter?
DPF residual ash is the small amount of non-combustible material left behind once a filter has regenerated. A little build-up over the life of a diesel is normal. Soot burns off during a successful regen, ash doesn’t. It stays in the filter and gradually takes up more of the space exhaust gases need to pass through, as DVSA’s own guidance on diesel particulate filters explains.
On this Audi, the ash reading was well beyond the safe limit, which explains both the grey smoke and why the filter kept trying, and failing, to regenerate on its own.
Why Ash Builds Up Faster on High-Mileage Diesels
Every diesel builds up some ash as it ages, it’s a normal by-product of burning diesel and of the regeneration process itself. At 273,854 miles, this Audi has been through a huge number of regeneration cycles over its life, and each one leaves a small amount of ash behind. Over time that adds up. No forced regen clears ash, only a proper clean or a filter replacement will.
Whilst in attendance we gave it an Engine Carbon Clean to get the source of the dirt entering the DPF in future nice and clean and help extend the overall life of the vehicle.
With the service overdue an oil change is now going to be done on Monday and we can then return to clean, flush and recalibrate the DPF with our DPF Clean service.
