Ok I have an 03 FX4 with front ABS. Had to replace both front bearings, did the pass. side first, no problems.
Then replaced the drivers side couple of weeks later (damn things aren't cheap). Then I had the ABS light start coming on every once in a while, I figured something was messed up in the hub assy.
Now that winter has hit, and I've put the truck into 4WD, the ABS light hasn't come on since.
Does the ABS work with the 4WD somehow?
Thanks.

 

You really dont want ABS in the winter anyway, at least in snow.

Most common issue is the rear abs sensor, although since you just replaced bearings with sensors its possible one isnt working right. Downside is that the dealer is needed to pull the codes and 100 to just read them I dont think its worth it yet.

IMHO, replace the rear abs speed sensor on the diff. Its about 20 bucks and takes about 5 minutes.

The 4wabs 4wd trucks also have a "g switch" that measures movement so it knows if all 4 wheels lock and your moving. The 2 systems are not really linked but this is as close as they get.

 

Thanks for the reply.
Where exactly on the diff is the sensor? I'll try that first like you said, if that's not the problem, looks like I'm replacing that drivers side hub. Still under warranty so...

 

This makes me wonder about my 4X4 ... I just put it up on jack stands and put it in first gear and then I hit the brake and the ABS light came on. Hopefully when I unhook the battery it'll reset it's self.

 

It the only sensor on the top of the rear diff. All you will need is a 3/8 ratchet with a small extension.