This is actually for my 00 Jeep, but I am sure they work similar.....

I changed the rotors and after my ABS has been messed up. My question is do the speed sensors work like a magnet or does it use some other way to detect movement? Also, would a failed wheel sensor show up on a scan if the Check Engine light is not on, but the ABS light is on? Would be nice to know what sensor is messed up rather than guessing.

I have a feeling I may know what happened, I used PB Blaster to loosen the rotors, along with heat, to get them off. Either the PB hurt them, or maybe just got them dirty. Also possible if it is a magnet sensor that old rust is stuck to it, lots of rust scales were flying when I was beating on the old rotors. I plan on pulling the wheels tomorrow and check to see if cleaning them helps, but once again I would rather know which one (if it is just one) is the culprit.

 

The tone ring makes contact with the bottom of the sensor. I do not know all the technicals about them. It will set off the ABS light. When i did the ball joints on my mom's 2001 Yukon XL, the sensor was in there so good that i just had to yank it out and it ended up breaking it, because she does not like ABS and the sensor is about $100, she is in no rush to purchase a new one for me to put in. My truck only has rear-wheel abs, and i am glad, because i hate abs.

 

The wheel sensors in an ABS system rely on the Hall Effect to generate either an A/C signal or a pulse train (system dependent) as the tone ring rotates under the sensor. No ... it should not actually touch the sensor but the gap value is critical.

A faulty ABS will not set a CEL but should store fault codes in the ABS computer. A DRB III scanner should be able to retrieve them but you'll need to go to the shop for that to happen ($$$).

The chances of messing up a tone ring and not knowing it are remote. It is much more likely that you damaged a sensor during removal. If you have access to an oscilloscope, you could probe the wire from each sensor, spin that wheel and watch for a signal.

 

i had my rotors changed on my 99 ram 2500 by the dealer and since then the abs and parking brake light comes on if i go over 60mph. went back to the dealer and that said they dont know and want to charge $80 n hour to figure it out still no luck.

 

Since the front ABS sensors (you DO have 4 wheel ABS, yes?) are integral to the hub/rotor assembly on 3/4 ton Rams ... I would start looking there.

Better idea ... since it's more than likely that the dealer messed it up, they need to find out what the problem is and fix it ... WITHOUT charging you.