You have a GT1, but you provide no faults. How do you expect us to help you?

Here are some troubleshooting hints for you.

Use the DIS service function, and perform ride height calibration. Clear fault memory in EHC2, and reset the flat tire monitoring system. Road test the vehicle a few meters, and let the vehicle fall asleep,(ignition off for 16 minutes)

Restart the car, and attemp to lower and raise the vehicle. If the light flashes, check the fault memory. If the fault memory shows deviation in ride height. More than likely you have a faulty EHC2 control unit. Here is how to verify.

Goto control unit functions, and select diagnosis request.
View deviation in ride height, record the readings for each corner.
View ride height sensor voltage, and record the readings also for each corner.
Now goto control unit function, and lower the front and rear together 1 time.
Goto control unit functions, and select diagnosis request again.
View the deviation in ride height, and more than likely only 3 of them have changed.
The one that has not changed will probably show 0, and must be investigated.

At this point, you either have
1) faulty ride height sensor
2) faulty EHC2 control unit.
3) incorrect installation of the sensor

Lets rule out #1 by comparing the current voltage reading of the ride level sensor to the original reading made before we lowered the vehicle. If the voltage has changed in anyway, then it is most likely fine. The EHC2 control unit can read the voltage, but cannot determine how much height deviation in millimeters. This is due to the control unit failure. The next step is to replace the EHC2 control unit, encode and perform ride height calibration. If the height deviation is readable, then the fault lies in the installation position of the ride height sensor arm.