TTEC 4825 ABS or Anti-locking brake system.

                                           
                                          Anti-lock Braking System

                               Anti-Lock Braking system on-stand

                             Indification pins of ECU from manual

                                    Connected to pin 20-LF sensor

              Pattern of LF sensor on oscilloscope 50V division, we have 100V

                                         On multimeter i see 3.2V

                                           Connected to pin 2N RF

                           The oscilloscope measures roughly 125V

                                              Multimeter-2.7V

                                            Connected to pin 2R-LR

                                        Oscilloscope shows rougly 85V

                                                 Multimeter-4.1V

                                              Connected pin 2S-RR

                                                i see roughly 90V

                                                   Multimeter-2.9V

                                           i have slightly holded the wheel

               With slow rotation of wheel, the sensor is prodused low voltage.

ABS does work in normal operation and we can see saim pressure in hydraulic system

                                         One wheel is slightly stopped

        and i activited hydraulic pressure in system by pressed brake pedal.

 The hydraulic pressure in ABS system reacts, when signal from two speed sensors   have
changed

A good wheel speed sensors typically produce alternating current (50-700 voltage AC) voltage readings, the wheel is rotating at about one per second speed. 

On the multimeter we can't see exactly what going on with speed sensors in ABS system.

The best method to check the wheel speed sensor is used oscilloscope.

A range of wheel speed sensor pattern, showing a typical AC sine wave pattern changes are in the frequency and amplitude with the wheel speed.  When the wheels turn faster, while the frequency and amplitude of the signal should be increased. On the sensor ring damaged or missing teeth will appear as a flat location or sine wave pattern gap. A crank or hub will have a change in the pattern of ups and downs as the revolution sensor signal strength of each change.
Different gap on speed sensors can occurs different voltage.

What exactly do the speed sensors inside of ABS system i will 

explain"on-car Opel Astra"

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