ABS pump relay waveform

ABS Self test:

When we switch the ignition on ... ABS does a selfcheck in order to see whether all the components are working , there is a 12 volts is supplied to the pin number 1H of the ABS control module and also to the fail safe relay , at this point the ABS warning light has a 12 volt supply from the pin number 2L and thru the fail safe relay to ground so the light is on . The ABS control module checks most of the components of the ABS unit except for the parts it can not check like the ABS wheel speed sensors which cannot be checked while the car is stationary.
When the failsafe is switched the ground side of the warning light gets a 12 volt supply voltage which in fact turns of the light as there is no flow of current thru the light. The fail safe ground is on pin 2J which shows this relay is earth triggered so if there is any problems with any of the components or circuit ... the ABS control module doesnt trigger the failsafe relay and the ABS warning light on the dash would stay on ! this will tell the driver that the ABS has found a fault and is not working , also if there is no issues it will be turned off and tell the driver that the ABS is working .

Create a fault:

We used a part of a plastic pipe to slow down one of the wheels while we were braking on the ABS demonstrator and the ABS control module picks this up as one of the wheels is slowing down faster than the others or thinks its going to lock up ... ABS control module prevents this from happening by closing the inlet valve via a solenoid on the wheel so there is no more extra pressure is being applied, then if this doesn't speed up the wheel to match the other 3 wheels, it will also open the outlet valve via solenoid to release the pressure on the particular wheel so it can speed back up and not lock up .

ABS Solenoid actuating:

Left front solenoid pin : ....... 1B

Right front solenoid pin : ..... 1C

Left rear solenoid pin: .......... 1D

Right rear solenoid pin : ....... 1A

we can get this info by looking at the ABS demonstrator wiring diagram which i have put the particular part of the diagram under ...

This is the Right rear solenoid pin 1A which has been actuated to either close the inlet valve so the pressure on the wheel slowing down is not increasing so it can match the other wheels or open the outlet valve to release pressure so the wheel wouldn't lock up .