I have a 99 F-150 lariet 4x4, a couple monthes ago the abs light would come on the first time the truck started moving from park, I replaced both front wheel bearings and the rear speed sensor, presto, fixed! A couple of days ago I went to start the truck and you know how the dash lights come on whe you first turn the key and then disappear, well the abs light stays on constantly... I checked the connections to all the speed sensors and made sure there was no moisture in them... My question now is, whats my next step?

Thanks,
Willie

 

Have the code read.

 

if you figure out what the problem is let me know! i have the same problem in my 2000 f150...

 

Yep, have the code read, and check out a list of codes like the ones in ALLDATAdiy to isolate your issue. It will save you money in the long run from just replacing parts in the system.

 

on startup, the computer checks to see you have continuity thru the wire and pickup. If not, the light turns on immediately. Once you start moving, the computer checks to see that the pickup is reading "movement" If no speed is noted when you go about 5 MPH, then the light comes on meaning a pickup is bad.... Yours could be a computer problem, but more likely a bad connection... one common place is the two prong connector to the front hubs. If you get it sideways just a little, it wil bend one of the small pins and crush it inside the connector, then read failure.

 

My '02 FX4 had same problem and wheel bearing replacement
was the fix about two weeks ago. Fingers are crossed that
I won't have recurring issue with ABS light !

 

You can make a resistance check of any of the sensors to test for a gross (open) failure. I posted the readings a few years back but I don't recall them off-hand.

Generally, if it's open, it's bad - pretty much the same test the 4WABS controller runs during POST.

 

I have had the same problem on my 99 f-150 4x4 sounds like a bad sensor on one of the front wheels.my problem started after I put new brake rotors and calipers on I had to beat the hell out the rotors to get them loose in doing so I fractured one of the wheel sensors. I suspect you may have done just the same thing I did since you put new wheel bearings in you have to tare down to about the same to do bearings.pull the wheel sensors out very carefully if they are old they brake easy you can try cleaning them and see if it helps but if not one or both are bad. hope this helps?