Hi Les,

I'd steer clear of this car, I'm afraid. That engine had major issues with stretching timing chains that was never truly fixed. If the chain stretches too far, it can cause catastrophic engine damage. Even before that, it's very expensive to replace the chain. Bizarrely, Mazda's solution to the known issue was to add a warning system that flashed the DPF warning light, which is why the two things seem to be interlinked and they're not. The issue then is, of course, many people see the DPF light and think their car needs to be driven at high revs to clear the filter. That only worsens the chain. 

In short, unless the chain has just been done and you plan on keeping the car for a finite amount of time, stay away from that generation of Mazda6 2.2 diesel.