hiya,
very common problem with saxos.
I'm guessing the aerial you have replaced is the one attached to the steering column? i know it sounds daft but some folk would think the roof aerial is the receiver lol
Where did u buy the transponder from...new/second hand?
previous experience....take key & slide it along outer casing underneath steering column as really thats the only thing i've had to do with previous saxo's.
hope it helps....
Scott, Fife
April 2010