Principle of operation, speedsignal
Principle of operation, speed signal |
Wheel speed |
The speed signal is obtained from pin 7 of the ABS control module and applied to pin 9 of the MOTRONIC control module.
The signal is a square wave with a voltage which varies between 0 and B+ and a frequency which varies with wheel speed.
Rotating the front RH wheel will suffice to check the signal. Among other things, the signal is used for idling control up to 900 rpm when the speed of the car is less than 3 km/h.
If the control module does not receive a speed signal for any reason, the CHECK ENGINE lamp (MIL) will light up.