Got back to the house, and did an Extended diagnostic code read. This is the first time I've had any codes show up doing the deeper diagnostic code reading, and I have two codes ETM-917F and ETM-951F. With multiple codes, according to the table, it points to code ETM-951F as being the main culprit....

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the key is sending out the correct signal I don't think you could confirm your remote sent CORRECT signal. Signal include high frequency and low frequency (modulation). I believe your RF part is still works correct, but digital signal unfortunately crushed. Actually, this is common issue for 2008-2...

Can you send me VIN, or public it here... for first.

I think we can transfer data from your original CDM to used CDM. You can send us PCBs only, but you have to mark each to exclude confusing. Also, if you have soldering experience, you can do it yourself, just transfer couple chips from your original pcb to used one.

If your UEM has issue inside like shorted CAN bus, yes, it could affect on start, but I do not think new UEM has some issues. ))
UEM responsible for: remote control option, TPMS, SRS belts lamp, it has blind sensor for adjustable mirror, also it control alarm system and interior lights.

Most possible solution is new key.
Most likely your original key lost synchronization to CEM. It is common issue for 2008-2009 P1 platform.