I have a vauxhall signum 1.9tdci on a 2006 plate. Problems started last year when the car started dropping into limp mode. I was able to turn the engine off and on again which would clear the warning light, the car would run fine again for a few miles,before dropping back into limp mode. This would carry on for a few days, then the car would smoke a lot for a few miles, but it would then clear the problem for a few weeks before repeating all over again. I had a diagnosis done, no error codes just a dpf problem was found. I was told as I was only doing short journeys the car was getting clogged up, and to try and force a regen. Which I did, and car was fine for a while. Then problems stated again, but this time when you turned the engine off and on it wouldn't reset itself and was stuck in permanent limp mode, the car also was struggling to start from cold. Had another diagnosis done still no error code. I had a new dpf filter and pressure sensor fitted to the car and it ran perfect for two weeks,then the same problems began again. It seems to happen more when doing faster mph than when just pottering around at low speeds.Car has had a new egr valve just before I brought it two years ago. Does anybody have any ides as to what it could be, don't want to keep chucking money at it. Thanks