Hey guys, new to the world of Audi. I’m a former tech of Toyota and Nissan. I found a pretty decently priced 05 S4 for sale. Guy doesn’t know whats wrong with it. It was running and driving fine, and now all of the sudden no start/turn over. Put the key in ign, all the dash lights come on, turn key: nothing but a click sound (kinda sounds like a relay clock). No power going to the starter. Can make the car turn over with a power probe. Has the following codes:

18080 Fan 1 control circuit/Open circuit/short circuit to- ground no signal/communication
18308: Fan 2 control circuit/Open circuit/short circuit to- ground no signal/communication
18036: databus drivetrain, missing message from steering angel sensor-implausible signal
18107: databus drivetrain, missing message from steering Column electronics-implausible signal
00688: vehicle voltage terminal-30 voltage supply to low
00466: steering column electronics control module- J527 - no communication
01300: Control module for navigation with CD- mechanism J401- No communication

any thoughts, repair suggestions, help would be appreciated. Looking to try and buy this car very soon if I can get a feel for what’s wrong.

Thanks!
- Jay