92 lumina 3.1

excellent car but now low coolant light comes on,have burped coolant &cleaned sensor which is only 1 year old ,put in with new rad.,no apparent leaks,not getting hot,fan does not come on except with a/c,even when motor is killed after driving.do'nt know if e.c.m. is lying to idiot light or going bad since have the fan problem too,how to check harness and sensor(s) with volt/ohm meter,or whether to just take it in and let someone else ****with it.

Welcome to AF. If the radiator and jar are at the right level, then the sensor is giving a false reading to the dash gage, has nothing to do with the pcm. Fan will not come on till 222 degrees.