The nice thing about GM and all other codes is they are grouped. The leading letter means something.
P = Power train
B = Body
B0242 is the air flow recirculation door driver circuit failure
B1242 is showing up as CD player focus malfunction
B1242 Air Flow Recirculation Door Driver Circuit Failure
Depends on where you look. Likely in the 98 Regal, this is going to be a recirc door issue. There was a stepping count number that they addressed on the air mix actuators and maybe on the recirc doors as well from 97 to 98. Wouldn't surprise me to learn that they built in the code for it.
Try going from auto to recirc etc and listen for a sound change in the fan noise and or a difference the airflow.
00 Regal GS: All kinds of cool stuff.