Engine Performance problem
2002 Ford Focus 4 cyl Front Wheel Drive Manual 153000 miles

I have the good old 1.8 tdci 115 bhp in my ford focus , recently it has been chucking the glow plug light on the dash board on , goes into limp mode and then stalls , had it read by someone who is not really experienced enough to give a good diagnosis, recent new dmf fitted sensor cleaaned , injectors have been drop tested? EGR has been inspected and is free, i've been told of the coolant sensor possibly at fault - i've noticed the rad fans coming on when driving along with no loading on engine ? dmf has cost best part of £500 to replace and i'm not sure i want to waste any more money on the car ?? please help