Volkswagen’s scheme to cheat on emissions tests could have been found out earlier if the automaker—and indeed all automakers—hadn’t been able to block car-owners from digging into the software that runs their vehicles, digital rights advocates say.

The Electronic Frontier Foundation (EFF) says that the Digital Millennium Copyright Act (DMCA)—the controversial US law governing digital copyright preventions—prevents tinkerers from examining or modifying the computer code that controls everything from the engine’s throttle to the brakes, and even the steering.

Car-owners who attempt to even inspect this code, much less modify it, are blocked by digital protections that only authorized mechanics can penetrate—and any attempt to break through those locks could violate warranties and other legal covenants.

The EFF has pushed the US government to make an exemption to the law, enabling car-owners to examine their cars’ software the same way they might check the oil or replace mechanical parts: After all, it’s their car.

The organization also cites incidents, like the hacking of a Jeep’s control system or problems that led some Toyotas to accelerate out of control, that might have been nipped in the bud if the auto hackers could have seen the code. That’s the same dynamic that results in software bugs and security exploits often being discovered by friendly hackers before the government or corporations suspect there’s anything wrong.

In the case of Volkswagen, cars with diesel engines were equipped with software that determined when they were undergoing Environmental Protection Agency testing for carbon emissions. During a test, the software would turn off mechanisms that increased engine performance, thus decreasing emissions; under normal driving conditions, the performance enhancement would be turned on and emissions were higher. Volkswagen CEO Martin Winterkorn resigned today in the wake of the allegations.

EFF attorney Kit Walsh suggests that watchdogs might have discovered this trick had they been allowed to examine the Volkswagen’s software. But so far, that push to exempt car software from digital copyright rules has gone nowhere. Indeed, the EPA itself wrote in to oppose the EFF’s arguments, writing that in its experience (pdf), more people would use access to the auto software to turn off environmental protections and max out engine performance, not tweak their engines for a cleaner drive—or, for that matter, to hunt for corporate malfeasance.