I had the red DPF full message appear, telling me to visit the dealer. I took Captain Allan’s advice given above in this conversation. My XF had entered limp mode. I took it on a 70 mile drive on the A38, trying to keep the revs as high as possible. The warning light stayed on for the whole journey but, when I switched off the engine on my return and left it for 10 minutes, the car was fine again and had returned to normal performance. Thanks for the tip!!