Campaigners have said car makers should not be protected from independent scrutiny of their software by copyright laws.
The call follows the discovery that Volkswagen had coded some of its diesel cars to cut nitrous oxide emissions when tested in lab conditions.
Had researchers been able to look at the source code, The Electronic Frontier Foundation suggests the scandal could have been uncovered earlier.
Chief executive at Volkswagen, Martin Winterkorn, has resigned after admitting his company had fitted computer-controlled “defeat devices” to more than 11 million vehicles.
In the US the Digital Millennium Copyright Act prevents people from avoiding “technological protection measures” that restrict access to copyrighted works. This includes reverse engineering the machine code in products to turn it into a higher-level computer language that can be understood by humans.
Security researchers in the UK face similar restrictions.
A tech consultant at Davies Murphy Group said there were good reasons for the industry to resist the pressure to share its code.
He said: “Modern cars are heavily computer-controlled.
“The computer code may well be controlling emissions, but it’s also controlling safety features like when your air bags fire and anti-lock braking systems.
“There is an argument for stopping people fiddling with those systems, because if you don’t know what you are doing – or even worse do know and have malicious intent – you could create genuine safety issues.”