IBM PCjr Manual page 254

It takes almost three minutes to test
your modem. After your IBM PC/r
has finished testing your modem, the
First IBM PC/r Test Menu Screen
appears with a message under Test
Tag "G". The meaning of that
message is shown below:
» Your modem is operating
correctly. Go to Step 3.
A Your IBM PC/r does not know
you have a Modem attached.
Make sure your Internal Modem
is not connected to your
telephone jack. If it is not
connected to yom telephone
jack, have your IBM PCyr
serviced. See "Service
Information" in this section.
B Have your IBM PCyr serviced.
See "Service Information" in
this section.
6-112 Internal Modem Test
Your Modem detected a dial
tone. If your telephone line is
connected to your Modem,
discoimect it and go to
"Running the IBM PCyr Tests"
in this section and select the
Modem test again. If your
telephone line is not connected
to your Modem, have your IBM
PCyr serviced. See "Service
Information" in this section.