Error code 42 + active spoiler problem

Genn'a UK spec has a problem with the active spoiler. Sometimes when the car has just been started the active spoiler will come down and go back up a couple of times. It's more likely to happen if the car is slowly moving forward and turning tightly to the right. The last time it did it the MIL came on so I checked for diagnostic codes and 42 was recorded.

Anyone have any suggestions on the likely cause or ways of identifying the problem? Being a UK it's not got a dodgy speedo converter. Is it easy (and more importantly cheap!) to replace the speed sensor?

Have you tried the option of joining the wire from the speedo to the odo output. From what I recall it has a buffer circuit, while this is not ideal it might provide a solution.

I haven't, but yes you're right it is buffered. That would put the fault in the speedo rather than the sensor I guess, or, as the dash has been out a few times for a blue LED conversion, I wonder if something has shorted or a plug is not back in securely?

From recent experience after having my dash out, the code 42 was caused by the dreaded pink wire pushing out a bit where it went into the connector at the back of the odo. I simply repositioned the wire properly in its connector.

Before I touched the wiring I disabled the alarm system and disconnected the battery.