Yes, the O2 heaters only come on when the engine is cold. The purpose is to heat up the O2 sensors so they work quicker.

Yes, won't cause adverse affects other than increased emissions when the engine is cold.

Yes, you will fail annual inspection because of it.

And I suspect those Densos aren't compatible, but I can't be sure. Original equipment is Bosch.

1998 Sportage - Gone.
2004 Honda Civic Coupe.
2007 Suzuki Grand Vitara - She got it.