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Diagnostic data link

Diagnostic data link

The ABS control module is not connected to a bus. Diagnostic communication takes place over a lead from pin 11 of the ABS control module to pin 8 of the data link connector (diagnostic socket) and from there direct to the diagnostic tool.

The diagnostic tool communicates digitally and serially with the ABS. Digitally means that the difference in voltage between the lead and earth has two values, in this case about 0 V and B+. The information is coded so that different combinations of 0 V and B+ pulses have different meanings.

Serially means that the information is sent in “packets” one after the other in very quick succession.

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.