It is funny you should ask.
I am changing mine this weekend. ($30 at the dealer).
First I am going to try to clean it as I am told by others.
If that does not work, then I will change it.
I have not seen it, but I am told it is located on top of the rear diff.
Clean the area around it first so no dirt falls in.
There is 1 screw to take out and then gently pull it out or pry it up.
ALWAYS ALWAYS ALWAYS make sure your socket/wrench is the right size or you will strip the head. Even if you have to lightly tap ot on.
My 99 F150 XLT 4X4 ABS is kicking in at 10KM/HR on pavement.
No check engine codes or ABS warning light come on at all.
If this does not work, then I will have to take it in as the expensive ABS sensors ($230 at the dealer each) on the front bearing are the next thing to try. (The whole front hub with ABS sensor on it is $330)
I am told it may be a ground issue or even some other ABS parts.
Right now I just pulled the #25 fuse out from under the dash for the ABS.
Breaking still work great but you have no ABS for winter driving.
It's the 4th 5 amp fuse down from the top right side.
On my truck anyhow. It is in your truck manual.
Your ABS light will stay on and it will not work anymore.
Truck brakes great though but you will not have ABS for the winter.
Its very easy to change the rear ABS sensor. It is bolted on with one 3/8 bolt on the top right side of the diff. Ford wants $38. for one. Napa is $15. and I've seen them for $12. on line. Clean around it good so crud does not fall into your gearing. The plug is a simple pull. You can change one in 5 minutes. On my 99 the #18 fuse according to the owners manual is for the ABS. There is also the control module under the dash. Another owner said that a bad rear brake light can cause your ABS/Brake light to come on. I'm curious what front sensor are you talking about. I have 2WD not 4WD. Is that a sensor for 4X4s? Oh and the dealer wants $110 just to change a 12. plug in sensor.
I picked up a new sensor yesterday at a local auto parts for $19. and even got a 10% military discount. Took only a few minutes to climb under my 99 F150 and change it. The one bolt that holds it on was a 3/8ths. If its stuck use a flat tip or gasket knife to gently pry it loose. Slip in the new sensor, bolt it down, plug it in and your done. Since Ford wants $110. to fix these you just saved $85.