my99accord

Hello, my 99 accord showed a code for bad O2 sensor heater. Tested it (open circuit), so I changed it. Still showing the bad code. Went through the diagnostics from the repair manual, and the conclusion is to try with a different, known good ECU. I beleive that the new ECU needs to be reprogrammed if I want to swap it. I have a few questions that hopefully someone here can answer.

I know I need to reprogram the keys to the new immo chip (or get an immo bypass chip) I also see that one needs to reprogram the VIN number.

1. Why does the new ECU need the VIN number if the keys are reprogrammed to it? If the immo system is happy, what prevents the car from running? The manual shows that with a 'donor' ECU and corresponding key, one can tie the two keys together and start the car.

2. Also, when getting a replacement ECU, is it enough to match the part number? How do I know it's programmed for the fed, non-California standards? Does it matter? I know the O2 sensor is different for CA (Ultra Low Emission Vehicle) and non CA.

3. Lastly, from much reading I believe the odomoeter data is in the instrument panel, not on the ECU. Can someone confirm this?

Thanks in advance

my99accord

UPDATE.

Got a used ECU, matching it with the 02 sensor of my car (the type with many holes) therefore the non-CA ECU.
Changed the immo board with an emulator one, so all my keys work with no need to reprogram.

All works well. Unplugged the o2 sensor and got the expected error code. Reset and done!

I hope this helps others.