2009 freightliner cascadia with Webco ABS system, abs light on

That’s a one nut supposedly foolproof system.Need to be checked with dial indicator for exact end play

 

I thought 1 time use

 

I found this yesterday on my rear grain trailer.
The ABS light would come on when it was damp out. A few days of dry roads and the light would go out. I did have a code for the curbside sensor.
Hidden in the plastic loomex was a connector to join the ABS sensor wire to an extention cable that went to the trailer ecu. Found evidence of corrosion from water penetration. It didn't look too bad, but I checked the other side and it looked shiny brand new.
I replaced both the sensor and extention cable. And the light went out.
Not the same sort of error the OP is getting, but just one of the things that can go wrong for others.

 

I just went through same thing. Replaced sensor first unfortunately then cable. Replaced other side cable. Kept old good one for future testing and diagnosis. Very intimidating at first. But was able to fix a few different issues on Truck and Trailer. Mostly bad wires. Took a little research but not too complicated. Hardest part was diagnosing which side sensor blink code referred to. Depends on type of valve and mounted position.