P2002 particulate filter efficiency below threshold

[Crazy Dazz]

I never even realised they had a DPF, but guess it makes sense.

What does it actually do when it regenerates? I'm guessing it burns the soot, but how?

I've read that if the DPF gets too badly clogged, the computer will not initiate regeneration, to avoid potential damage?

Are these easy problems to fix?

Reason I'm asking is that I've been looking at a cheap old Mondeo (2010) that is known to have a DPF problem. (Engine light on, and codes indicate that the DPF won't regenerate.)