We have found that when this happens it most likely to be a wheel speed sensor .
Best way to diagnose this is to drive with a good scan tool with ABS live data ,
custom the four wheel sensor to one list and do a good test drive ,when you see the ABS light flicker or come on check the speed
on the data list one of the four speed may drop out to 0 mph.
If it does this then you know which wheel sensor has failed .
If all stay the same then next possible issue could be your alternator ,battery connections .or power supply to the ABS module .
So also in live data change the data list to ABS voltage and check that you have 14.+/-.5 volts at all time .do test drive as before only you will be checking the voltage ,if drops check connection to ABS model ,alternator out put and wiring harness condition.
repair where needed if wiring damage .
If no damage and voltage is good suspect ABS model .
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Kind regards Greg.