The code readers that they have are absolute junk, all they can read is Check engine lights. You can do one a few things,
1. Get on the horn with people in your area and find someone who has a good code reader, one that will do diagnostics, view parameters, buzz test, all that good stuff and see if they will scan your truck. (this will be your cheapest option) I have a good friend on here that met me and scanned my entire truck for me for free, but I still paid him. He has an Autoenginuity (best bang for the buck...around $360)
2. Put a deposit on a scan tool from oriely's...the one near my house has a decent one that they loan out.
3. If I were you and had the money I would order an Autoenginuty scan tool ( it is software that goes on a laptop) it will seriously pay for itself
4. Go to the dealer...I don't recommend this. I went before my friend scanned mine and all I asked for them to do was to Read the ABS code to me....they returned with that will be $90. I laughed and walked out. So 4 trips to the dealer to get codes read and you can buy a scan tool....better yet you can make a little side dough off of it here and there to offset the cost more.
Hope this helps....
also there is a abs sensor on top of the rear diff...take it out clean it and reinstall. They get small metal shavings on them (common) and the shavings set the sensor off. A new one is like $18-20 at a parts store. The front ones are around $100 depending on where you go
The ABS system is good and bad on these trucks, it doesn't take much to set them off but the good thing is, the truck runs a diagnostic every 5 mins so after you do some trouble shooting, give it time and drive it down the road and back to allow it to reset the light. Just replaced my front 2 hubs and sensors because the left front went out...it took it 5 mins or so to go out after replacing it and has been off ever since
Sorry for the long winded post, just trying to help you out