Speed Signal

Wheel speed
The speed signal is taken from the ABS control module pin 26 and goes in to the Motronic control module pin 9.
The signal, which is a square wave, has a voltage that varies between 0 and B+ volts and a frequency that varies with the wheel speed.
To be able to check the signal you just need to rotate the right front wheel. The signal is used for instance to change the idling speed to 900 rpm when the speed is lower than 3 km/h.
If the control module for some reason does not receive the speed signal, the CHECK ENGINE lamp (MIL) will come on.