On the ESA control, error/fault codes are read from the LED or display on the main control board. Error 4 points to an obstruction-detection / motor-feedback fault: the control is not seeing the expected encoder/motor signal through a full open-close travel. Confirm no physical obstruction in the track, that the belt tension is correct, and that the motor and encoder connectors are fully seated. A common cause is incorrect jumper / parameter settings — verify the configuration jumpers match the door type, then run a fresh learn cycle so the control re-maps the door’s travel. If the fault persists after a clean learn, suspect the motor/MDU or control board.