Just occasionally the dealer has the equipment to sort out problems like this. My BMW with ABS gave me problems and I reluctantly took it to a dealer. There were several things actually wrong with the darned system, but it came back working fine. Have courage!

 

I'm going to let the dealer do a flush of the front brakes and see if that resolves the issue...

 

There are a lot of electronics in ABS, so get them to check the entire system thoroughly.

 

Let us know the outcome, could be good info. for the ABS of us.

 

Will do!