The RABS doesn't compare the axle speed to anything - it has to look at decel rate and speed to sense lockup. I believe the RABS is independent of and functions the same no matter the rest of the powertrain.

 

So, it's only looking at the speed (pulses) of the tone ring and doesn't compare to actual road speed in any way?
I guess I will just disable it.

 

Implying it has it's own integral decelerometer in it that was accurate enough to provide that capability. I'm surprised that they had tech accurate enough at a price point to make it economical to do 25 years ago. I'm not saying it doesn't work that way, I'm saying I'm really impressed that they did it

 

No accelerometer. It's all based on rate of change of the rear axle speed. There has to be a programmed rate of change curve where if the actual rate of change is above the limit, lockup is inferred and brake pressure is modulated until ROC is back above the threshold. For example if rear wheelspeed drops from 50mph to 30mph in 1/2 second and based on a programmed maximum deceleration rate the same speed reduction for the same speed change is 2 seconds, the computer knows that the wheels are beginning to lock and reduces line pressure until speed goes back up above the curve.

 

That's a pretty simple approach, and probably a lot more reliable. Smart cookies those engineers.