There will usually be a sign of a serious problem. The brake pedal may be difficult to press down or the brakes may lock up without warning. There may also be a strange clicking sound when you apply the brakes. Whatever the symptom, it is usually accompanied by the ABS warning light on the dashboard. If you need a second mechanical opinion, try one of our reader-rated Good Garages: good-garage-guide.honestjohn.co.uk