Hi Simon. We have just had a 2004 Tiptronic Sprinter in for non start / no crank.

The Garage that sent it to us found out that they could start it by removing the cover on the starter relay ( under the seat ) and pushing the contacts together.

Ours turned out to be a water damaged Tiptronic ecu under the seat, ( They had Steam Cleaned it inside ) The Circuit board was green and mouldy and had rotted away beyond repair.

We fitted a New ecu ( in the region of £400 + )
And at that point, we could not program it, We also found that the relay contacts were sticking together and causing the dash to stay lit up continuously and draining the battery. We Replaced the relay and it then allowed us to program it up and it ran perfectly.

H.T.H. Tony.