99 Dodge Ram 1500 ABS

Hi all
My freind has a 99 Ram 1500 4x4 and the ABS, and Brake light is on constant. This model has ABS in the rear only, i think the only thing working this is the module next to the master cylinder, and a speed sensor, could it be in the rear axle, anyway any one know how this works, and what to do to fix it..thanks

Going back a few years, I had a chev that the brake light came on. If my memory is good, and it ain't , I think there was a way to get the error code.

what it is, is a speed sensor is located on top of your rear end which which a gear on the inside to let it know how fast you are going. If that sensor goes bad (which is very tyipcal I already repalced mine in my 2001 at 65K miles) it will throw the abs light. It is a dealer part for $40-50 depending on your area. It is very easy to replace it has an electrical connection on top then one bolt you back out. Takes about 5 mins to do yourself if the electrical conenction comes undone nicely and easily.

If its not that then it could be a couple different things but pretty much 90% of the time its just a bad sensor. But heres a possible list if the sensor does not fix it.

Open up the rear end and look for chunks could be broken clutch packs which is also common.
Also could be missing some teeth on the tone wheel (the sensor reads the teeh not common to break unless you offroad heavily).
Could be bad wiring going from your abs module to your sensor.
Could be bad abs module.

But like I said 90% of the time it is the sensor if not then open up and look for chunks.