2014 Q50S with direct adaptive steering. After car crash this car was towed to service, where this car got worst possible treatment. Firstly they removed battery for some reason and when inserting it in the place did not inserted it all the way down and when they closed hood, battery posts hit hood metal and shorted. After that car stopped responding to key. wheel stuck at 90 deg. angle. Then this car stayed there at service for couple of months and then they brought car to me. After inspecting car I replaced shot Ignition fuse and car started responding, but failed to start. Didn't recognized the key. When I performed key writing I was able to start the engine. There was couple of short fuses which I replaced. Car drives normally except steering is very hard. Now to diagnostic data. All seems OK, except error code C1138 - 4 Wheel Active Steer (4WAS) Circuit. Also Car does not drives faster than 80 km/h. which I believe is safe mode due to faulty steering. Digging deeper I found that DAST2 module is not showing up in module list when you read errors. I can see it in the list of modules when I perform coding. Writing part number to DAST 2 did not return any errors and by the looks of it successfully completed. Live data from diagnostic showing that Backup Circuit A and B STAT2 (which means lack of communication on backup circuits). Also strange thing is that when I turn steering wheel to right I get normal angles but when I turn wheel left after zero steering angle and pinion angle gets 117000 degrees. I checked continuity between 17 and 22 posts on all modules and there are OK, I checked steering wheel angle sensor, I checked all fuses and fusible links. DAST calibration mode 1 working OK and correctly finishes, but mode 2 gives message that can't perform calibration because requirements not met. Now I stuck in predicament, ordering new Steering sub module is very long process and I'm even not sure that module is faulty. Also it is quite expensive. Is there any way to test Steering Control Sub Module on stand? With multi meter or oscilloscope?

I had a similar crash car in a few years ago, only the main module behind the glove box talks to the CANbus. The two sub-modules are on a separate high-speed Flexray bus, so they don't show up as discrete CAN entities.

Eventually I fixed it. There was 2 separate issues. First issue was that Steering Control Sub Module plugs had loose connector pins female part. I found that totally by accident. So I took needle and pushed the springs just a nudge. Second issue was me doing DAST calibration wrong. Turned out that you need to perform calibration 2 times followed by steering angle center point setup. Correct procedure is as follows.
(I did this on Autel MaxiSys)
1. Clear all errors from DAST1 and EPS (DAST3).
2. Go to Control Module -> EPS (DAST3) -> Special Functions -> DAST Calibration (Mode1)
3. Hook up battery charger, Gears on P, Motor Off, Ignition On, Car lifted so front wheels are off the ground.
4. Start calibration. When steering wheel stops adjust it to neutral position and press start again.
5. Turn off the car for about 10 seconds.
6. Repeat 2-4. Do not turn off the car this time.
7. Go to Control Module -> ABS -> Steering Angle Center
8. Erase any errors if there is any.

Hope that helps. DM me if you have questions.