99 Expedition ABS light

When I start the truck the light is off. Once the truck starts to move that is when the light comes on. If I turn the truck off then on again the light goes out until the truck moves again. Any ideas about what the problem is?
Thanks.

If the ABS light is on at anytime while driving then you will need to get the ABS system scanned for diagnostic codes which will lead you in the right direction.

I have the 1999 and I check the usual stuff. Brake fluid, it was a little low and topping if off did not help. I checked the diag code at Autozone and nothing! So, I read some other posts about the rear differential sensor. I removed the unit and measured with an ohmmeter. It read infinite resistance, in other words an OPEN circuit. I then went to Pep Boys and thay actually HAD the part! I brought along my ohmmeter and measured the resistance and sure enough, mine was bad. A new sensor read about 300 ohms ? (I forget the exact number). So I bought the part (like $15). Installed in the differential and now my ABS light stays off! So before you bring to the dealer you can pull that unit out and at least measure it. If it read either ZERO ohms (shorted) or infinite is is BAD. Hope this helps others!:smile:

Correct, Anytime the ABS light comes ON after car moves the cause is a Wheel speed sensors in 4 channel ABS system or on 3 channel ABS sytem the Differential Speed sensor or either front Wheel speed sensors.
Glad you found the problem without spending alot of money, But sucks for us Ford dealers. I could of made some money with that.

And you know what? I would have brought this to the dealer to fix but I am getting rid of the vehicle in like 6 months or so. I certainly did not want to drop a few hunderd dollars, or maybe more. Some dealers might not just replace the sensor. They might go for the more expensive stuff and that is just not right. Most people don't know enough about their vehicle and sometimes unscrupulous dealers/shops will take advantage :uhoh: