Death triangle in Prius 1st Gen.

Have a mod 2003 prius wihich has been amazing all those years. Not a problem. It has now only 85 500Km (53 000mi). But lately I felt some shaking in the wheel when turning left. I read somewhere it was due to the low battery. So I charged the batetry overnight and the problem desapeared. But some 2 weeks later it came back. So I took it to a revision (repair shop) not with the official dealer, The repair shop diagnosed the steering rack problem, costing more than 5000€. I changed the battery and the problem desapeared again. but some 10 days later I had the death triangle, the PS sign and the engine ALWAYS ON.
Now the car runs turns right and left smoothly but I can not make the dumb death signals desapear.
Can someone out there help me with this problem? I deeply apreciate any help, because I am not fully convinced the real problem is the faulty steering rack.

 

Thanks Brian, for your kind help.
I´m going to get an OBD diagnostic tester and see what the real problem is. I had, long years ago, an alarm installed by a Toyota dealer and hope this is not causing problems: because when I connected back the 12 V battery, I neard relays clicking and lights coming ON, and had to open and close the doors with the command to reset those relays and lights.

 

I connected the OBD tester, erased errors and car runs perfect. Thanks for the precious help.

 

Code erased P3191, as well as the death triangle and PS! sign