You recently diagnosed an “antiskid service required" warning on a Volvo XC90 as being due to different sized tyres front to back, but there may be a different reason. When my 2006 Volvo S60 was about three years old the “antiskid service required" warning would illuminate followed, the next time the car was started, by "antiskid temporarily off.” However, this latter warning would clear after driving a short distance. Repeated annual visits to the Volvo dealer failed to provide a solution, although on one occasion a connection on one of the wheel sensors was cleaned and a software upgrade applied, and this produced a respite of about nine months. Finally (when the car was five years old) the problem was diagnosed as a faulty steering angle sensor. This was replaced and the Volvo dealer gave some financial assistance with the final bill (including the diagnostics cost) being just under £800. No further problems have occurred.