I have Thermador Pro Grand 30" Pro-Style All-Gas Range with 4 Star Burners with the 2 XLO simmer setting.
All four burners work including the 2XLO simmer modes.
For some reason the Blue Burner light on the left side (XLO knobs) stays lit even when the range is fully off. I’ve tested all the features of each burner and they work.
Unfortunately Thermador did not provide any technical information like the wiring diagram and/or parts list for this model. Whith lack of such information we are not able to help you with the troubleshooting.