Originally posted by MarkO:

Not true. One is heated, the other isn't and I cant quite remember which is which. I think the lower (post precat) is heated. Dont quote me on that though.



According to the wiring diagram, they are all heated.

According to my visual inspection, they all have 4 wires. (Unheated oxygen sensors, which I've only seen on two vehicles, both mid-80s carbureted models, only have one wire.).

According to Bosch, Autozone, and http://www.oxygensensors.com the universal replacement is the same part number for both applications, front and rear.