As regards the fault code descriptions, I think you may be getting confused between the engine and the trans. Either that or Autodata is even worse than I thought.

The speed sensor is in the gearbox, in whats commonly known as the electric pack.

The usual cause of the speed sensor code is the speed sensor signal. The first thing to check is for trans fluid in the trans plug. If you have fluid here you need to change the socket the plug goes into and its O ring, clean up the loom as best possible. If you have fluid here you should also check for trans fluid at the other end of the loom at he ecu plug and in the control unit itself.
The second common cause of this code is the electric pack in the trans. If you need to change it you need to drop the trans sump and valve chest. Simple enough job.

If there is fluid in the plug you could clean it, charge the customer and let him off warning him it might need an electric pack or you could just fit both the pack and the new socket.

It would be worth your while learning these systems as there are loads of them around and they give plenty of problems. Its also a good idea to do a glycol test on any you work on. I would think google would have lots of info on this.