I have a 1997 F150 4.6 V8 and i have recently gotten a check engine light and the codes are for the rear oxygen sensor on both sides. I checked a few wire diagrams and it showed that there is 4 wires going the oxygen sensor: 1 gray, 1 black, and 2 whites.
Now the whites are for the heater part, and 1 white should be a 12volt wire and the other white should be the heater ground. Heres the problem, both of my white wires have 12volts going to them. Is it possible there is a short or what. I am really confused! All help would be great thanks.

 

If I understand you correctly, 12 volts on both sides of the OX sensor heaters is an indication that ground is missing.
No short or a feed fuse would blow.
This code fault condition makes the PCM unable to test the cats efficiency.

 

Correct. The PCM grounds one side of the HO2S (HEGO) heater to warm it up. If you read 12V on both sides, the PCM isn't grounding it at that moment. I'm not familiar with the specifics of the programming, but it's conceivable that it only grounds it when it detects the engine is turning, like it does with the fuel pump relay.

 

What code(s) are you getting? A heater circuit malfunction in the rear sensors will not necessarily illuminate the SES light .

 

I am getting these codes:

P0141
O2 sensor heater
circuit malfunction
(bank 1 sensor 2)

P0161
o2 sensor heater
circuit malfunction
(bank 2 sensor 2)