Originally Posted by rwenzing
This is risky. Ford started using "fast light-off" oxygen sensors on many models after 1999. The FLO heater element gets the sensor up to operating temperature faster so that effective closed-loop emission control may begin sooner after a cold start.
The PCM-controlled heater timing is calibrated to match the heater type, so using a 2000+ sensor in a 1999-back vehicle may cause the sensor to overheat and burn out the heating element.
That is quite an interesting information you have there. As you know, my uncle is also having similar idea with thedustcloud. At first, he was having a hard time to find the ford oxygen sensor location
and later found out he needs a replacement of it but since he wants to save money, he was also able to find a replacement of oxygen sensor from an older model in a near junkyard but kinda worried if it will work. Having read this post, it seems my uncle has no choice but to go ahead and buy a new replacement of it. Thanks for this helpful tip.