2002 Pontiac Grand Am PO141 code retrieved

what is the mv on the o2 reading,should fluctuate between 350-550 mv,that will show if the 02 is working,if not Disconnect the HO2S 2 connector.
Connect a test lamp between the ignition 1 voltage circuit and a good ground. turn the ign on tha probe that circuit with a test light.if it lights test the ignition 1 voltage circuit and the HO2S 2 heater low control circuit.command the 02 heater on/off see if the test light lights,if it does it needs an 02 sensor.if you have a modis this should do bi directional tests like commanding the heater element on/off in the 02 sensor.if the test light doesnt light could be an open/high resistence or short to ground in the circuit.post back with what you find.

On the modis, Bank 1, senser 1 reads 700-800 fluctuating, Bank 2, senser 1 reads, after warming up, around 500-600.

these 02 sensors have a range 0f 0-1000 mv,it the range they operate in.you might have a heater element not functioning in the 02 sensor,the modis should be able to test this.read the above post and test that 02 sensor the way I outlined.post back with what you find.