I was browsing through the hookup guide for SparkFun's OBD-II UART breakout and found something particularly worrying written half way down in a quite casually presented way:
Keep in mind when you upload this to your board, you will want to disconnect the OBD-II board RX line from the Arduino TX-0, to prevent issues during code upload, such as bricking the OBD-II board.
For my money I think bricking your device should come with a more stark warning than one stuffed part way down a guide starting with "keep in mind" and continuing with "issues". Nonetheless it caught my attention as I tend to build sealed boxes that aren't sprawled in front of a keyboard ready to be rewired any time a re-flash might happen.
Is the real risk here the fact that all of the flashed data would stream past the RX pin of the UART board and potentially accidentally send a 'self-destruct' signal? (Also I'm not sure a system is really up to scratch if you can accidentally tell it to kill itself.)
Surely the programming port is not the one being borrowed by the UART hookup? On a MEGA 2560, using a different serial port, is this still a risk or is that only on boards with one serial port?