Thanks for your commentIt could be programmed for the wrong wheel size, though that is quite a big difference.
Sorry, no. I think somebody here should be able to tell you if it is possible and how.If it is wrong do you know how to reset it ?
I’ve taken it back to Halfords but they confirm the correct ecu has been fitted so there is nothing they can do. They suggest I take it to another branchIn your other post, you suggested the controller wasn't applying the power correctly either and suspected Halfords might have fitted the wrong replacement controller.
So your new controller doesn't apply power in the same way as your old controller, and the bike now doesn't achieve 15.5mph as it should either.
If it were me, I'd take the bike back to Halfords again.