[shorod]

Does your Sable have a button in the instrument cluster for "Traction control On/Off"? If so, that may explain the discrepancy you're seeing relating to dump valves for all four wheels versus a shared valve for the rear. I'd also suggest you try turning off the traction control and see if the same thing happens when braking. I'd also suggest you check for proper operation of the brake lights and, using FORscan, check for toggling of the Brake Pedal Position sensor as you press and release the brake pedal.

If all four wheel speed sensors are tracking one another, and none of them drop rapidly or raise, then drop, when approaching the speed where the ABS activates, I'm at a loss for what would cause the solenoids to trigger.

Other than the pulsating brake pedal, do you notice a change in braking effectiveness? If the ABS were engaging due to a wheel speed issue, I'd expect you to notice a surge during braking due to one or more brake calipers releasing.

The ABS module is located underneath the battery tray.

-Rod