Engine Fault?

Hi, I have got a 2005 Citroen Xsara Picasso. I recently had the EGR valve replaced, but since I got the car back, the engine management light doesn't come on, but when I start the engine, "Engine Fault" comes up on the dash for a few seconds then goes off again. If I stop the car and keep the engine running, all is ok until someone opens any car door, then "Engine Fault" comes up again for a few seconds, then off again. Any Ideas PLEASE?