1990 ranger CEL Comes up code 41 KOER

[1990RangerS]

I have had an intermittent check engine light for a while and finally brought it to a friend who's got an OBD I scanner and we got a code 41 with a key on engine running test. The explanation that the scanner gave was "No exhaust gas oxygen (EGO) switching detected - always running lean." Anybody know what sensor(s) might be going bad?

 

[Earl43P]

O2 sensor before the catalytic converter (the only one you have).

Might also check Fuse #18 (15A).