answer on/to/about
I learned that the prepositions 'on' and 'about' are equal when used with the word 'answer', meaning "an answer on/about the subject of an question".

So is that true that 'on' and 'about' should be followed by more details, while 'to' don't have to ? Like:

1) An answer to my question.
2) An answer on my question about the cars repairing.

Question

answer on/to/about
I learned that the prepositions 'on' and 'about' are equal when used with the word 'answer', meaning "an answer on/about the subject of an question".

So is that true that 'on' and 'about' should be followed by more details, while 'to' don't have to ? Like:

1) An answer to my question.
2) An answer on my question about the cars repairing.

Answer

An "answer to" is more specific than an "answer about". Let me illustrate from a Trip Advisor post I just googled, which reads:

"I am trying to find out an answer about mattress firmness in this hotel."

The writer is seeking information about how firm the mattresses are there. Are they so soft that they will cause his bad back to become worse? He's trying to collect general feedback on what it was like to sleep in a bed at that hotel.

If he were investigating the mystery of why mattresses at that specific hotel were of a particular firmness, or perhaps how to adjust the mattress after he already had booked a room there, he would write that he was "trying to find out an answer to mattress firmness in this hotel".

Answer

The question seems a little unclear to me. Yes, the expressions "an answer to my question on car repair" and "an answer to my question about car repair" are equivalent. A person might even say "an answer to my car repair question". I hope that helps.