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Diagnostics communication

Diagnostics communication

ABS and SRS



The two systems which are not connected to a bus, ABS and SRS, are each connected to pin 8 of the data link connector by their own communications lead.

The diagnostic tool communicates digitally and serially with the selected system. Digital means that the voltage difference between the lead and ground has only two values, in this case roughly 0 V and B+. The information is coded so that different combinations of 0 V and B+ pulses have different meanings, e.g. whether the SRS or ABS is to be called.

Serial means that the information is sent in “packets” which are transmitted one after the other in rapid succession.

In cars with Traction Control the TC/ABS control module is connected to the P bus but diagnostics communication takes place via the K line.

Diagnostics

If none of the systems can be contacted, the fault may be either in the car or the diagnostic tool. If the diagnostic tool can contact one of the systems concerned in another car, then the fault is in the car.

In that case, first check that the control module is awake. The ABS and SRS warning lamps are tested by the control module as soon as the ignition is switched on. If the control module is awake, then the fault is probably in the lead between the data link connector and the control module.

If the Trionic cannot communicate with the TC/ABS for 3 seconds while driving, the diagnostic trouble code P1925 is generated.