Dont be rushing on getting a speedo converter or a cheap on of ebay as they can do damage to the auto!!!! I just found out mine was giving wrong readings to the autobox it comes up as the power button flashing when you turn the car on rather than lighting up and going out.
You need one thats made for auto boxs. In the diagnostic check you can do on the car it comes up saying speed sensor 2 is the dials and it sends a speed signal to the autobox you need a speed converter that ties in with this.
These guys do one for stageas!
KMH-MPH,the UK's leading speedometer conversion specialist