Four wire O2 sensor source car?

[Tom Cloud]

>>>Ford cars had "allways" heated oxygen sensors, as many japaneses 
>>>cars. 

>> don't know about Ford cars, but some early Ford trucks ('80's)
>> used 2-wire sensors

>Excuse my ignorance on this.  But what is the
>difference betwen a 4 wire and a 3 wire heated oxygen sensor...

just whether the heater and sensor have a wire in common
(3-wire) or not (4-wire)

Tom Cloud <cloud at peaches.ph.utexas.edu>