Carefully remove the rear wheel abs sensors and clean them. They are notorious for getting crudded up from brake dust and malfunctioning. While they're out, use a bright flashlight and while you rotate the wheel hub, look down the hole at the tone ring just to be sure no teeth have been broken off. If that doesn't work, do the same to the front. Chase the wires back to the the first connector for each and separate, then put some dielectric grease in one side of each and fully reconnect. This will prevent any water intrusion or contact corrosion in the future so you avoid that easter egg hunt down the road. If you have a multimeter, check the OHM read for each. Open, replace. I don't recall of the top of my head what the acceptable OHM range is, but usually it's and open that fails the sensor. Someone else may have that number or it's definitely in the service manual.
Still have a problem after that, there should be a U code in the ECU. Pull the fuse for the ABS pump and re insert to hard boot the system....sometimes that will fix. If not, you'll most likely have to spend to get the U code pulled so you know where the problem is.
