How do I fix the factory radio-antenna situation where I have no AM radio, when FM works fine?

car starts, runs and drives perfectly?
AC or heater blower works on high?
head lamps work fully and brightly.?
tail lamp (park) all glow? ?
brake lamps work and are bright.
check fuses?
look for connections to the radio loose or damaged

AM Radio dead means the antenna is missing wires to it bad. or missing.
FM may work say on 1 stations if the stations is like 5 miles away, all stations that are under say 25miles must work or the antenna is bad. FM, and vastly farther for AM.
we do not know where you live( a town) so can never guess
what stations are in range to you. see?

scanning for what?, not told ,AM, FM or SAT?
SCAN FAILING IS ANTENNA BAD.
(AT BEST) IT FELL OFF. THE WIRED CONNECTION MARKED ANTENNA
yes it does or FM radio will be dead. for sure!
some cars the connection is to windshield antenna
and then later windshield glass was replaced wrong
wrong glass or not plugged back in.
reading your service manual now
base radio only
SAT rec. is pin 37 roof antenna
FM rec is pin 75 ant.
with NAV or with out NAV
i will do NAV no. BOSE system factory
pin 81 window antenna AM/FM
pin 107 with NAV am/fm
as you cans see there are 4 options new
for RADIO head end and NAV choices.
we can not guess what is there.
now what you are scanning for.

FM need a good antenna, buT FM in the country side will be weak
or even dead, FM does not travel far at all ,even only 20 miles
AM we have super power stations that cover most the country.
I bet the RADIO is just fine.
it can be bench tested with a 1 strand of say 4 feet of wire for an antenna.
you posted about only a RADIO not CD and not AM
FM is short ranged, 88 to 108MHz. is that
no town told , but you can call your closest station and ask them there coverage, spec.? 50miles or 10 or? what ever.
or you can go to a 2nd car, test FM see if there is one strong station.
if not there there is none.
on home RADIO we use a roof mounted 30Ft high antenna, FM
and goes way father,.
in car that can not be done, most antenna amps in cars only increase noise.
is this your first car, or first ever FM radio.?
yes antenna's can fail even the ground, (it is 2 wire coax to fail)
the mount can corrode. the cable can be bad.
some have antenna in the wind shield glass, and some one puts in new glass with no antenna there well that fails hard.
FM is mostly a CITY BIG DEAL, no living in the sticks.
also there are tiny FM micro station,and those are weak.
only line get a FM map for you town, just like Cell phones but for FM.
radio. see what is there and its POWER/coverage.

bad antenna or lead in coax cable.
am can be heard in city with no antenna
but never fm , unless its like across the street. the transmission station.

Check the antenna connections.

bad radio. FM is harder than AM
but do try , 1 thing
remove the antenna plug from radio jack.
then add a 3foot long insulated wire, any wire
to the inside center jack pin, forming a temporary antenna.
no AM now? , then bad radio.
good now?, your antenna is bad.

If you FM stations are working fine, check the antenna connections because the AM stations depend on the antenna more than the FM stations do.

if you have a factory radio, then chance are you antenna is amplified (even if you don't have an antenna that goes up in the back). The fuse for the antenna amplifier could have blown or the amplifier itself my have gone bad. It could also be your radio but, i would check those things first... Just a side note: i don't know of any stations that around me that aren't odd numbers 92.3 fm,95.5 fm,100.3 fm. Where you able to tune it to 100 fm before?

get a new one as they are cheap these days!
& not worth the labour costs to try & fix them anymore!
Cheers Rob

Check mounting surfaces at antenna. Corrosion or looseness and the antenna loses its ground to the body.