I was calling around to get prices on a up stream O2 sensor from the local parts stores, when i decided I would try the dealer and they told me that my 2003 FX4 with a 5.4 could have 1 of 2 different sensors. 1 would have a Green connector and the other would have a Gray connector. Does anyone know the difference between the 2, and why wouldn't the parts stores know or have mentioned this? Any help would be great. Thanks

 

The front one is the oxygen sensor the second on is the catalyst monitor

 

You are correct. But when i asked the dealer I asked for the up stream one and that is what i was told is that there are 2 different ones for the up stream