It depends , what's the RPO - regular production order code ? Call the dealer with the code an they can tell you . Or hook up a up scale scan tool . one that will talk with all the modules on the computer . You could down load Forscan to you lap top an go on ebay an by a ELM327 wi-fi , this plugs into you OBD2 connector on the vehicle an communicates with the forscan scan tool . It shows all the computers on the vehicle . ELM327 V1 5 OBD II Bluetooth Car Diagnostic Interface Scanner
I dont think it's your anti theft. If you're having issues with it I would bypass it completely to eliminate that possibility allowing you to troubleshoot easier
The radiator has a built in transmission cooler, unhooking the transmission lines would have let the system loose fluid, from the lines and the cooler. Make sure your transmission is full of fluid.