My grandpa has a 06 F-150 FX4 . If I tap the brakes the tires lock up. He has had it to the dealer 6 times. They keep replacing sensors. It does not do it all the time.

 

Which sensors are they replacing?

 

ABS and one by the master cyl.

 

All 4 tires lock up at the sane time

 

How long has it been doing this?
As much as I hate saying it... It maybe time to consider a new dealer/shop.

I've seen "this" happen on a ABS valve body tester we made for a Popular brake system manuf. But the computer automated results seem to be a bit uhm...different than just "locking-up".

I'm sure more will chime in on other ideas to look at... but IMO I wouldn't touch it if its under warranty.

 

It has been doing this for about a month. We was in texas when it started had it at a dealer down there. They replaced a ABS senser. Got half way home Witch is ohio and did it again . Have had it to two defferet dealer ships up here. It is under warranty , the truck has 23,000 on it.The truck is at the dealer now will know something Tues.(MAYBE)