My Check Engine light came on and I took it the AutoZone and they checked it and gave me this response. How hard or easy is it to replace this sensor?
Apparently either:
1 the sensor is bad
2 the fuel system is running too rich or too lean
3 the engine misfired
4 the fuel pressure is very high or low

 

Post the actual fault code.

 

HO2S21 - Circuit Condition (Heated oxygen sensor bank 2 sensor1

 

That is not the code, that is a description.

The code would be in the format of Pnnnn where n= 0 to 9.
Example, P0172

 

P0153

 

P0153 - HO2S Sensor Circuit Slow Response (HO2S-21)

The chart ( that I have from 2002, should be the same ) points to DTC P0133 for the list of items.

The slow part would lead me to believe it is the O2 sensor itself, but checking the wiring to it, as well as the other items on the list should be done prior to spending the money ( I am in the group that thinks replacing o@ sensors every 60K miles is standard maintenance ).

few threads on the topic, if you do a site search on P0153, there are 41 threads on that alone. Searching for P0133 should provide additional ones.

https://www.f150online.com/forums/v8...ble-codes.html

https://www.f150online.com/forums/19...ensor-1-a.html

list of the items to check for the DTC
https://www.f150online.com/forums/v8...ode-153-a.html

Suggestion to replace them as pairs.
https://www.f150online.com/forums/v8...k-2-where.html

While it is generally accepted that the cause is the O2S itself, no member has replied to the thread to confirm that is all the repairs that were done to fix the code, so 41 suggestions 0 confirmed answers ( even 1 from a member I gave the DTC list to back in 2003, that had an exhst leak ).