Got a high impedance volt meter? Must be digital or tubes (VTVM).
If not, do NOT connect up anything to the O2 line.
95% of the time O2 sensors are not bad. They get fouled or poisoned, but rarely ever go bad, even over a lifetime.
Often another problem will make them lazy or read off, but correct that problem, get it hot, and often it will clear up and start to work again.
Code 45 is rich condition:
1.) Code 45 is set when the O2 sensor signal voltage remains above .7 volts for 30 seconds or more and in "closed loop".
2.) Engine time after start is one minute or more.
3.) Throttle position between 2 % and 20 %.
(stolen graciously from http://www.misterfixit.com/code45.htm
so evaluate what could make the exhaust rich, don't mess with the messenger, (the O2), mess with what would make it rich. Air filter, carb, float, fuel pump, PCV, charcoal vapor canister, bad or disconnected MAP sensor, etc.
How do ya tell it your 02 sensors bad or not? My 87 Brougham 307 gives me a code 45, but I'm not sure its correct.
Any Ideas would be appreciated.