We were called to diagnose a Mercedes Benz C180 W204, 2015 model with symptoms - no gear selection by selector, no gear selection in dashboard, and no crank or start.
We started off by first checking for fault codes using Xentry and it was found that there was no communication to the VGS/Transmission control unit which related to the no gear selection.
The ECM also showed fault codes for no communicatin to VGS, we checked for power supply to the VGS itself and it was found that no power was coming to the VGS, on this model, the VGS is supplied power by the front SAM/Signal Acquisition Module on terminal 87 which is an output.
The Output relay 87 was inspected and tested, and was found defective. The issue was resolved by replacing the defective relay and the vehicle is back on the road now.