It is universally understoof that a bad O2 sensor can lead to poor fuel economy and mis readings by your car's OBDII and ECU, however here is my question:

If the O2 sensor

1. ) Lost connection to the OBDII (i.e. the wires were damages or severed)

or

2.) The OBDII is just fried from extensive Use


Would the car throw a code? Or do you have to check out manually out of paranoia?

Thanks,