2003 Cadillac CTS STUCK ON PARK

I am assuming that it starts and runs, it just don't shift from park. Do the stop lamps operate correctly, this could be a visual indicator of a possible switch problem, and cause your concern. The shift lock solenoid is actually controlled by the rear integration module in response to brake switch status sent over the data bus from the EBCM(abs module). It could be that the rim is not recognizing the brake switch info, the ebcm is not sending the info, a faulty solenoid, or there is a circuit fault. If the brake lamps operate, you could simplify isolating a cause with a scan tool, the fact that the ABS light is coming on, may have some relation to the nature of the fault. I can brainstorm for you further, but would like the info on the stop lamps and whether or not they work.