I have a 54 plate Fiat Ducato Ci Carioca and the speedo has stopped working. I have just had the 5th gear repaired and the specialist had a look at the speedo cogs etc and assures me these are ok. He reckons it could be the transponder but is no expert on this type of job. He says it is electronic so there are no cables. Does anyone have any idea how to fix this? Many thanks in advance.