Speed Signal

The ABS control module sends a speed signal to pin 79 of the Motronic control module. This signal is a pulse train consisting of 92 pulses per wheel revolution. Each pulse has a duration of 60 micro seconds.

This speed signal is used to:
^ prevent adaptation of idle speed control when the car is in motion
^ determine whether the car is being driven on a "rough road" it misfiring is detected.

In the case of stationary wheels the ABS control module sends test signals having a frequency of 14.25 Hz.