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My 98 Honda accord-v6 failed in the smog test due to the check engine light caused by the fault code

P0141 - O2 sensor heater fault (Bank 1 Sensor 2)

I'm wondering

1. which O2 sensor this error message refers to?
2. will changing the O2 sensors fix the "Check Engine Light"?
3. do i need to take the car for another diagnostic check ?
3. How much does it cost to fix this?

Appreciate your help.

Thanks