Aunque + Subjunctive

Question

This topic requires a better explanation.  There is a question where one person talks about the condition of another’s car.  Both speaker and listener know the car’s condition.  According to my reading of the lesson (perhaps mistaken), this means the subjunctive is used.  So, I chose funcione but funciona was the correct choice.  So, doubt or uncertainty does not seem to be the deciding factor when considering the use of the subjunctive after aunque.  Thanks.

Accepted Answer

Hola Sean
I imagine you're referring to this specific question:
Tu coche no es muy nuevo, aunque ___ estupendamente. 
(Your car is not very new, although it works beautifully.)
For this test-question you have the hint saying:
"Hint: The speaker is declaring that "the car works beautifully"
When we are declaring some information, we mean that that piece of information is new to the person who is listening. In this case, it's assumed that there hasn't been a conversation going on between the two people where it was established that the car worked really well, in which case, you'd see the subjunctive in a sentence following that previous conversation: Tu coche no es muy nuevo aunque funcione estupendamente. 
This is why we're using the indicative instead in our test-question, because the case is different, the speaker is letting the owner of the car know that his car seems to work really well. It's a realisation in that precise moment, maybe because he's just had a ride in it and notices how well the car goes (despite not being a new car). 
I hope this clarified it. 
Saludos
Inma