I had the glow plug light on mine a while back now and it was the brake switch behind the brake pedal, I think I posted on it, 5 min job and under £20 sorted mine right out might be worth renewing that for 20 bucks first, instead of paying for a computer diagnosis
When the glow plug light flashes on a TDI, whilst the car is driving, it denotes a fault in the "engine management system". If the unique DPF light is on the DPF requires regeneration. As said above, the car needs to be plugged into a diagnostic tool to check what is wrong - the two faults may be linked. For example, a sensor fault somewhere may be preventing the DPF from regenerating naturally.