1999 FLD120 ABS light

I think some systems only had sensors on the rear most axle. The front axle just mimics the rear axle signals. You’ll need to find the ECU. If it has a bunk it’s underneath it, behind the passenger seat. If not, it should be in the cab somewhere. I think all Freightliner’s are in the cab. Probably has a vented plastic cover over it. If not it’s outside on the frame. Either way. Identity the ECU. It’s probably a D model. ECU should have a diagnostic switch Hold the switch for 1 second, release and count the flash codes on the dash. That’s a start. Next you’ll need to figure out what valves or valve package you have. It’s mounted on center of frame, in front of, or under the fifth wheel. It has wires from the ECU, and air lines running through it to the wheels. Might need to change the valve and add ringtone hubs. If the problem is only a bad wire or missing wire from ECU, to the valve, they usually are in sections. You’ll just have to figure out what you have, and figure out what you’re suppose to have. My guess is the ECU won’t need to be changed. Just missing the wires, or has the wrong modulator/valve ( old one from 6x2 set up) and has the hubs from the original front drive axle instead of the rear axle. My knowledge is very limited. Have used diagnostic blink codes to find a bad wire between the ECU and Modulator valve, and to diagnose a bad valve on one side of the double valve assembly. You may need to change your current double to a single. I don’t know. This website has all the info you should need to figure it out.

 

Here’s some examples from the website