Above 65mph the brakes on our car are very resistant when being pressed - what's the problem?

My son has a Mitsubishi Lancer which appears to run very well. However above 65mph the brakes seem to be very resistant when being pressed and need extra foot pressure, this can sometimes result in a sudden swerve one way. Below 65mph the brakes operate normally. When exceeding 70mph for a minute or two the ABS warning light appears on the dash panel. Once illuminated the car brakes correctly as if there is no problem. Can you suggest what the problem might be?
It could be that one of the ABS sensors (fitted to the brakes) is faulty. We would suggest that you find a local Good Garage and get them to either carry out a diagnostic to see if a fault code exists or to carry out a visual check on the actual ABS sensors. good-garage-guide.honestjohn.co.uk/
Answered by Alan Ross

Ask Honest John