Improvements relating to railroad telemetry and control system address problems in compatibility between HOT and EOT units, implement an automatic UDE location procedure, and automate calibration of EOT units. An improved two way protocol that allows EOT units having different code formats to be used with a HOT unit. A method is implemented by a HOT unit, cooperating with an EOT unit, for locating a fault which causes a UDE brake operation. An automatic calibration procedure for the EOT unit that does not require the operator to have access to the electronic circuitry.