You may not be getting a close limit signal from the bad rear door board. the controller will throw a 21 error and won't reset until it see's the CL from the board. You need to install a new board and do a learn sequence. Or the door board goes through a self check on power up. if the self check fails it will throw an error and the car won't run. Either way you need to replace the door board, and do a learn.
