1995 Taurus OBDI Check Engine Light On Code 172

My Taurus runs fine. The check engine light comes on a little while after I start the engine! The diagnostic trouble code reads 172, lack of heated oxygen sensor switches, indicates lean bank #1. This year I have replaced the cap, rotor, plugs, wires, both heated oxygen sensors, fuel filter, MAF sensor, fuel pressure regulator. I am satisfied that there are no vacuum leaks that I haven’t repaired! I reset the check engine light by disconnecting the ground cable for a few minutes.
How can I get the check engine light to stay off?