> Maybe just require a way to detect modification or emissions override, and anyone who does that pays the fine if they fail inspection, and for anyone else the manufacturer pays. They'd presumably be begging people to install modifications so they can hand off any fines...

For passenger vehicles (including diesel pickup trucks but not diesel semi tractors), after you buy it, if you make modifications to it, you the owner are now responsible for it. Also note that the diesel pickup truck is classified as a passenger vehicle rather than a commercial vehicle and so needs to meet the standards of a passenger vehicle.

However... where it gets interesting is when you switch to commercial and industrial equipment. In these cases, the manufacture is always responsible unless they go out of their way to lock it down.

For example, if you made a farm tractor and could adjust the software to change the fuel air mixture to optimize it for certain altitudes (farming at 5000 feet has different tuning than farming at sea level) then if it was possible for the person using it to change that... you, the manufacture are still responsible for any things with emissions. For industrial equipment, you need to lock it down to the point where the person doing it is knowingly violating warranties and regulations.

... And then you've got John Deere with its DRM on the firmware to make sure that farmers don't modify them to go racing ( https://youtu.be/hK-WO9SzVcs ) and get the company in trouble (and the EPA is less of an issue than someone modifying the settings for a combine and getting killed).

https://www.biren.com/blog/2020/september/defective-machiner...

> Products claims over defective industrial machines are subject to many of the common defenses in products cases, including comparative fault of the user or a third party (CACI No. 1207A and 1207B), misuse or modification (CACI No. 1245), and more.

> These claims may also become a target for the sophisticated user defense, in which a Defendant accused of failing to warn argues they are not liable because the Plaintiff is a sophisticated user who, because of their position, training, experience, knowledge, and / or skill, knew or should have known about a product’s risk of harm (CACI No. 1244).

> Overcoming such a defense requires assessment of what a user knew or should have known at the time of an accident. More importantly, Plaintiffs’ attorneys should anticipate such a defense when bringing a products liability claim over a Defendant’s failure to warn, and explore other alternatives for proving defects based on defective design or manufacturing, if supported by the facts, and especially if a Plaintiff may qualify as a sophisticated user.

That misuse or modification part - https://www.justia.com/trials-litigation/docs/caci/1200/1245... its a two part test where both parts must hold

> 1. The [product] was [misused/ [or] modified] after it left [name of defendant]’s possession; and

> 2. The [misuse/ [or] modification] was so highly extraordinary that it was not reasonably foreseeable to [name of defendant], and therefore should be considered as the sole cause of [name of plaintiff]’s harm.

Can one claim that changing the fuel settings on a tractor is extraordinary that it can't be reasonably foreseen? If not, then John Deere is still responsible unless they take every possible action to prevent it from happening.