My sons 95 F-150 4x4 5.0 put out a 565 "canister purge curcuit failure" , 172 & 173 "oxygen sensor not switching" during a self test off the check engine light. Anyone know what these mean and what the fix would be? We located the purge canister but are not sure where the solenoid or sensor for it is located, and I'm told there are three O2 sensors. Where are they located and how do you "test" them? Thanks

 

Canister purge vave is located in vacuum line going to throttle body area from canister to left of TB facing rear. Can remove and test with 12 v source and should click if free and working. Check wiring and connector for corrosion, etc.
Unless you have an early OBD II 96/very late 95 (check build date on door), It is unlikely you have 3 O2 sensors, just one. My sensor is in a boss close to crossover pipe by transmission with a pigtail going up. Just replace, dont know of any easy test, but can read voltage with proper equipment and digital meter.
Good luck.