config t
service internal
exit
test cellular 0 modem-power-cycle

You should receive message like the following:

000048: *Feb  8 16:04:50.975: %CISCO800-2-MODEM_REMOVAL_DETECTED: Cellular0 modem is now REMOVED
000049: *Feb  8 16:04:50.975: %CISCO800-2-CELLULAR_INTERFACE_NOT_SHUTDOWN: WARNING: Cellular0 interface sh
ould be shutdown before removing modem. Reload Required to reset interface
000050: *Feb  8 16:04:50.975: %CELLWAN-2-MODEM_DOWN: Cellular0 modem is DOWN
000051: *Feb  8 16:04:55.523: %CISCO800-2-MODEM_INSERTED_DETECTED: Cellular0 modem is now INSERTED
Modem Power cycled successfully