I’ve done a fair amount of research on this and find myself more confused then I was before. I have a 2001 ram 1500, automatic, 4wd, rear abs. When I first start the truck and drive it the abs/brake lights are off, however when coming to a stop I can hear a click under the hood and a a pulse to match the click in the brake pedal, and it gets slower as the truck slows down. When I’m at highway speeds at about 60, the abs/brake light come on and the clicking noise and pedal pulse under braking go away. My speedometer works just fine and I’ve replaced the sensor on the rear differential, which made no difference. Thank you in advanced for the help!

 

With only rear abs, the sensor on the rear diff is the only one you have to worry about. The clicking you hear is likely the dump valve for the rear abs. Why it is activating is the real mystery. How are your rear brakes??

 

The rear brakes are fine. Adjusted perfectly with plenty of life left in them. There’s never a change in the feel of the brake pedal. Meaning it never gets spongy or loses pressure. Just that slight pulse that goes along with the click under the hood. Once I hit about 60, the click and the pedal pulse go away and the abs/brake light come on. I’m at a loss!

 

If the lites are on, there should be a code to go along with it. Don't know if the local parts store scanners will read ABS codes though....

 

I have a pretty fancy scanner here at home and it’s not reading any codes.

 

Can it actually talk to the ABS?

Might try setting up your scanner to show you what the wheel speed sensors are reading. See if one of them is out of sync with the others.

 

On pre-CANBUS Chryslers the ABS, AIRBAG and other modules are on separate bus called CCD. Given that these vehicles are 15+ years old by now a lot of newer scanners don't even bother with CCD bus support. What tool do you have ?

On a rear-only ABS there is only one speed sensor on the rear axle. From the description it sounds like the ABS is very briefly kicking in under normal braking and the frequency is depending on the wheel rotation speed. That makes me think there is a problem with the speed sensor generating a consistent signal. Could be the tone ring is damaged, you might be able to see the ring with a mirror through the hole for the speed sensor. Better if you have an inspection camera, or maybe record a video with the phone.

 

I’m going to take the e sensor out today and see if I can get an eye on that tone ring because the clicking I’m hearing from under the hood is directly correlated with how fast the truck is moving, the faster im going the faster the clicks are

 

I tried the best i can to get my camera in there to see

 

Those teeth look a little chewed up. Any problems with the differential recently ? You probably should open it up and see what's going on.