So if a company tried to apply "Your code must meet emissions standards before you are allowed to install it" limitations via a license agreement, then it would conflict with both GPLv2 and v3. If a company only allowed you to instal after being signed by the company's own testing laboratories, it would conflict with GPLv3's TIVOization clauses.

But if the government says: "All software installed on car ECUs must meet emissions standards" then there is no conflict, infact this is already 'implied' by the current laws.

The GPLv3 'should' also be fine with a "All car ECUs must only accept software that is signed and approved by a 3rd party testing laboratory" law. You have the exact same barrier to installing software on the ECU as the actual manufacture of the car.

The main example where the GPLv3 might conflict with a government law, is when a law mandates "the car's ECU must be locked down in a way that only the original manufacture can change the software"