FCP said to send their sensor back for credit ($30), which seems very fair of them. Just installed a new OEM sensor from the dealer (such a deal, at only $75), and it works fine. FWIW, both ends of the connector between the sensor and chassis wiring were tight, and very clean and shiny, so I'm sure corrosion wasn't an issue. Now there are no fault codes, the fuel mixture properly leans as the engine reaches operating temp, the radiator fan works appropriately, etc., so the problem is solved. It would have been interesting to compare resistance measurements between the two sensors at various engine temps, but I just wanted to get done with this job and let my wife have her car back. I also had the pleasure to pay $8 (really, $8!!) for a thermostat seal at the dealer, rather than $0.50 anyplace else.

Dean