Big Evil ~
Thanks for the advice! I, too, was thinking that I should wait until the thermostat is replaced before venturing into troubleshooting other potential electronic gremlins that may be causing the O2 fault codes. Always start with the simplest problems, and you end up with simple solutions. ;-) Let's hope for now the thermostat is the culprit!
I'll post the results later this week. Here's hoping this thread will end itself there... Take care, and thanks again!