2000 Marquis throwing codes on all 4 O2 sensors
 

102,000 miles. Engine light always on Code reader shows heater fail on all 4 O2 sensors.
Checked for shorts, found none so far. Checked and all fuses good

Is it possible that all 4 failed at same time??

Not likely that four sensors will fail at the same time. There probably is a fuse just for the O2 sensors's heater circuit. Otherwise, check wiring to make sure the O2 sensors are receiving power and have a good ground.