Vauxhall zafira 2.0 tdi (2004) ?

Hi can any one help?? My 2004 zafira 2.0 tdi traction control light flashes when I reach 40 mph, the car seams to loose power when the light is flashing, then when the car reaches around 70 - 80 mph the light stays on and my abs light comes on and stays on, when both lights are on perminant the car seams to run fine no loss of power at all, soon as I turn the engine off and restart the car all the lights are back to normal until I hit 40, any help would be great full as this has baffled me, cheers Andy