Diagnostic data link: Diagnosis
If the system cannot be contacted, the fault could be either in the car or in the diagnostic tool. If the diagnostic tool can contact the same system in another car, then the fault is lies with the car.
First check that the control module is active; ABS warning lamps are tested by the control module as soon as the ignition is switched on. If the control module is active, the fault is probably to be found in the lead between the data link connector (diagnostic socket) and the control module.