Modifying your car software is considered fair use. Here is something i posted in other thread:
It's perfectly legal, at least for now
Yes, read the article. The article quoted (New DMCA Exemptions Mean You Can Now Hack Your Own Car) is from 2015 and The Library of Congress DID allow hacking and modification
Here:
https://www.gpo.gov/fdsys/pkg/FR-2015-10-28/pdf/2015-27212.pdf#page=10
"Proposed Class 21: This proposed class would allow circumvention of TPMs protecting computer programs that control the functioning of a motorized land vehicle, including personal automobiles, commercial motor vehicles, and agricultural machinery, for purposes of lawful diagnosis and repair, or aftermarket personalization, modification, or other improvement. Under the exemption as proposed, circumvention would be allowed when undertaken by or on behalf of the lawful owner of the vehicle."