ABS Sensors and hub assemblies
 

Is there a way to test the ABS sensors to know definitively whether they are good or bad?

Also, is there a way to determine if the hub assembly is bad (short of pulling it off for visual inspection)? Jack it up and see if there's any play in the wheel? Spin it and listen for anything unusual?

Trying to confirm a diagnosis before I start throwing parts at it!

Not sure on the ABS, but for your hub assemblies jacking it up and checking for play should determine whether or not they should be changed.

When i checked my Wrangler i personally checked it then took it to a brake shop to have them confirm, which they did free of charge. Took it home replaced myself.

Ill tell you what, hubs are a simple change but can be a pain! I haven't touched a disco's but my Jeep needed an impact wrench for the axle nut, and a 3 jaw puller to pry the SOB hub out. Hope you dont need to change them!

The factory spec says to torque the hub/axle nut to 360 Ft/lbs, and I think most run-of-the-mill impact wrenches are only about 240 Ft/lbs! The factory manual also says to pull the hub and the axle and then use a press to separate them. BUT, a 3-jaw puller will do the job on the Disco too.

I know it will be a b!tch of a job, but I'll do it myself to save the $$$ on labor. Plus, Will Tillery has used hub assemblies for $115 (shipped) and offers a 1yr warranty on them.

FWIW, I had a bad front sensor output code a while back. The hub seemed perfectly fine, it had no play in it and made no noise. I wasn't sure if it was the sensor or hub so I just kept driving it. Probably around 1k miles or so later the hub bearing started making noise while driving and turning, telling me the hub was definitely bad (though it still had no play in it when checking it). So the hub might be bad, it just takes a while for it to show itself - that sensor must be very sensitive. BTW the hub was pretty easy to replace.

Its not that its difficult to replace, just takes some elbow grease! As for the impact wrench it will definitely work, just pick up a cheap one from harbor freight. I soaked the axle nut in penetrating oil overnight the next day hit it with the impact wrench and within a few seconds it was off. When you replace it be sure to load up the threading with anti-seize. It is definitely worth the money you save though, for my jeep i got quoted like 1900 (hub assembly, wheel cylinders, pads, shoes, and rebuilding a caliper, rotors), for parts and labor, i ended up spending about 400 to do it myself.

Yes, any ABS Wheel Speed Sensor can be tested. On Discovery's they are a 2 wire sensor, attach a Volt meter to both wires and turn the wheel. You should see an alternating current (+/-). It is even better if you use an oscilloscope to see the AC wave. Also, by looking at the wave you can see if you have any bad teeth on the reluctor wheel.