Since your getting the 604E, I would check the wiring and connectors at the RDC unit. Could be loose, corroded, or bent pins. If they are good, then replace the sensor.
Here is a link that shows how to test the sensor itself using a multi meter. You may want to consider doing this to see if the sensor itself is the issue.
https://www.2carpros.com/articles/abs-wheel-speed-sensor-test
Hope this helps. Let me know how you make out.
Joe
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Monday, March 23rd, 2020 AT 12:56 PM