Have you looked at IATF 16949? You could not audit that alone, it would make no sense. It is additional rules, and it needs the main rules to function.
ISO9001 is a set of rules that defines a healthy, functioning QMS in ANY process organization. (I did not say manufacturing, one of the main reasons for the big release change is they want to start using it in the medical service industry, ergo a lot of the manufacturing language in it has been replaced).
Anyway, ISO9001 is the baseline.
Then the International Automotive Task Force (IATF) said "Well, this is a good start, but OUR industry has a few nuances in it that ALSO should be done ..." and that is what is in IATF 16949. Other types of industries have different riders.
All of them are set up in this way: Do everything that ISO9001 says, but then ALSO do this additional stuff.