From time to time, when I start the car the message "Anti-skid service required" appears together with the warning triangle. both go out when I push the READ button on the left hand stalk. The next time I start the car the message "Anti-skid temporarily off" appears. This time the warning triangle will not go out. However, after driving about 400 yards, both disappear. My local dealer can never find any fault - neither message is displayed by the time the car gets into the workshop. What is the problem?