How do you reset the check engine light?
take a battery cable off
Most auto parts stores have a check engine light reader that you can borrow for free to read the code and also to reset the check engine light. If they are not busy, they may even do it for you for free. Support your local parts store! Worst case: Take it to your dealer or buy a check engine light reader that can also reset it.
I think you are assuming that to reset the check engine light you can just disconnect the battery. Disconnecting the battery on a 2004 OBD2 compliant vehicle will not reset the check engine light. It must be reset with an OBD2 scan tool. This would work on OBD1 vehicle but not on OBD2 vehicles. So the radio issue is mute. Have the problem that set the check engine light repaired and then reset the light…